Storage overview

At a Glance
• Storage Networking Technology
• Direct Attached Storage
• Network Attached Storage
• Storage Area Network
• Storage Devices and Technologies
• Network Devices
• Fiber Channel
• Zoning
• Storage Virtualization
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Data Creation & Storage (1/2)
• Data & Information
– Swelling rate/volume of data created by individuals/businesses.
• Value of Information to Businesses (Discussion)
– Business value from individuals’ data
• Example: On-line job search engine.
– Identifying new business opportunities.
• Examples: (1) Buying/spending patterns: Retail stores,
Supermarkets, (2) Customer satisfaction/service: Tracking
shipments & deliveries.
– Identifying patterns that lead to changes in existing business.
• Examples: (1) Targeted marketing campaigns: Communicate to
bank customers with high checking account balances about a
special savings plan, (2) Reduced cost: Optimizing utilization of
vehicles and gas which are used by a Delivery service.
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Data Creation & Storage (2/2)
• Data Storage
– Growth in need to store the data over longer periods of time
with improved accessibility.
• Example: Need of banks to store customer’s old account details.
– IT expenditure on Storage has increased proportionally.
• IT budgets typically have to include expenditure on Servers,
Networks, Storage, and Personnel.
– Where to Store?
• Cameras, MP3 players, Laptop hard drives, USB drives, CDROM/
DVDs, Employee workstations, Servers, Disk arrays, Tapes, etc.
– Data Storage can be Centralized or De-Centralized.
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De-centralized Storage
• With advances in networking, client-server model enables
business units within an enterprise to have access to their
own servers and storage.
• Pros
– Applications no longer had to wait in one central queue for
data access and execution.
• Cons
– Leads to fragmentation of information (islands of information)
thus making it difficult to enforce uniform processes and
policies, as well as to manage.
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Centralized Storage
• Data is stored and accessed by different applications in/from
single location.
• Pros & Cons
– Data can be more easily managed, shared and protected.
– Data can be made highly available.
– Applications need to wait in one central queue for data access
and execution.
• Challenges in Information Management
– Planning for capacity growth (Information growth is relentless)
– Classifying data (Value of information changes over time)
– Address data availability
– Security
• Example: Networked storage, DAS.
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Storage Networking (1/8)
• Link multiple storage devices together (centralized data
repository) and connect them to other IT networks.
• Users can access data through high-speed connections.
• Benefits
– Consolidation
– Improved Performance and Reliability.
– Easy data back-up for disaster recovery purposes.
– Increased Data Availability
– Better use of IT resources
– Data sharing and improved asset usage
– Can be used with storage management technologies
• E.g. Storage Resource management software, Virtualization,
Compression
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• Networked storage environment consists of
– Application servers
– Storage arrays (Disk Arrays)
– External hardware interfaces within the application servers &
Cabling
– Storage fabric between the servers and the arrays (for SANs)
• Popular Storage System Technologies
– Block Level Storage (E.g. SAN)
– File Level Storage (E.g. NAS)
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• Deduplication
– Elimination of redundant information on a same storage area.
– File Level Storage
• If any Files are identical throughout the storage area, redundant
copies are eliminated.
• But if File-1 is 10% (say) different from File-2, then both are saved.
– Block level Storage
• Divides each files into many blocks, if any blocks are identical
throughout the storage area, the redundant copies are eliminated.
This method reduces considerably the spaced used for many files
with similar information.
• Example: If File-1 and File-2 are 90% similar, only the 10% that is
not similar from the “File-2” is modified and stored, reducing
considerably the space used.
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• Backup
– Both levels offer incremental back-up solution.
– If all the information from the storage has already been
backed up to a remote location and later the file is modified,
• File Level Storage: Backup the complete new version of the file.
• Block level Storage: Backup only the desired block of file which I
modified and not backed-up earlier. This reduces the size of the
backup and the amount of data being transfer during the
process.
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• File Level Storage
– Used in home computers & smaller business systems.
– Files and Folders are stored/accessed in bulk.
– Disks configured with file-based protocols like NFS, SMB/CIFS,
NCP.
– NAS devices have stripped OS (E.g. FreeNAS) that can be
configured/controlled over the network using a browser.
– Simple to use/implement and comparatively inexpensive to be
maintained.
– “Scale Out NAS” incorporates a distributed file system that can
scale a single volume up to several petabytes (1015) all while
handling thousands of clients. As capacity is scaled out,
performance is scaled up.
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• Block Level Storage
– Used in larger business & enterprises.
– To the user, storage will appear basically as another hard drive
on their machine, although it is on a remote location. This hard
drive can be formatted, partitioned, used to run an OS, fixed to
one user, etc.
– Data transportation is much efficient and reliable.
– Raw volumes of storage are created and each block can be
controlled (as an independent Disk drive) by server based OS.
– Most likely will have dedicated personnel to setup and maintain
the system.
– Offers boot-up of systems which are connected to them.
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• Block Level Storage (contd.)
– Uses iSCSI and FCoE protocols for data transfer as SCSI
commands act as communication interface in between the
initiator and the target.
– Used to store files and can work as storage for special
applications like Databases and Virtual machine file systems.
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• Summary
– Block level storage is very flexible and offers high performance
(depending on use case) but comes at a prize of more complex
management, harder to set up and is more expensive.
– File level storage is easy to set up and manage and it offers
relatively cheap mass storage compared to block level, but
performance could be an issue and user access and
permissions need to be configured on the file level storage
device itself which might need a little getting used to.
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Interface Technologies (1/4)
• Interface can be device/program which enables user to
communicate with a computer/system.
• Interface Technologies include
– Internet SCSI (iSCSI)
– Serial-attached SCSI (SAS)
– Fiber Channel (FC)
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• iSCSI (internet SCSI)
– Distance between disk array to a node (server or switch):
Unlimited, however, latencies increase as distances increase
– Scalability: Limits to the number of devices. Can scale up with
10GbE technology (for larger enterprises).
– Performance: 1GB/s
– Investment: Low
– Used in small & medium sized Businesses owing to low cost and
simplicity.
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• Serial-attached SCSI (SAS)
– Distance between disk array to a node (server or switch): 8m
between devices
– Scalability: 32-65,535 devices
– Performance: 3GB/s (2004) to 22.5GB/s (2017)
– Investment: Medium Cost
– Requires no dedicated cabling and can run over existing IP
infrastructure.
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• Fiber Channel (FC)
– Distance between disk array to a node (server or switch): 50km
– Scalability: 256 devices, 16 million devices with the use of
switched fabric (SANs)
– Performance: 4GB/s to 128GB/s
– Investment: High Cost
– Used for its excellent performance, availability and scalability.
Commonly used in large data centers.
– FC over Ethernet (FCoE) uses Data Center Bridging (DCB)
technology to encapsulate FC protocol within Ethernet
packets.
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Internal and External DAS (1/2)
• Most basic block level storage where storage devices are
directly connected to host via an internal/external
connection.
• Storage devices are dedicated and either reside as an
integrated part of the host computer (e.g., hard drives,
removable storage devices, etc.) or directly connected to a
single server externally (such as RAID arrays).
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External Direct
Connect
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Internal and External DAS (2/2)
• Internal DAS
– Viable option for small environments because it is relatively
easy to deploy and inexpensive in simple configurations.
• External DAS
– Ideal for localized data connectivity in environments with a
single host or a few hosts. i.e. Small businesses or
departments and workgroups that do not need to share
information over long distances or across an enterprise.
• Offers ease of management and administration
– Internal DAS: DAS is handled by the server/client’s OS.
– External DAS: DAS is handled by a management interface to
the intelligent array housing the storage.
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Networked Environment of DAS (1/2)
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Client 2
Server A
Application A
Server B
Application B
Server C
Application C
Disks for Server A
Disks for Server B
Disks for Server C
Client 3
Client 1
Local Area
Network
SCSI
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Networked Environment of DAS (2/2)
• Same connectivity port on the Disk array cannot be shared
between multiple servers.
• Clients connect to the Servers through the LAN.
• DAS connectivity uses protocols such as ATA (IDE) and SCSI.
• The distance between the Server and the Disk array is
governed by the SCSI limitations.
• Applications
– Small companies traditionally utilize DAS for data serving and
email.
– Larger enterprises may leverage DAS for mission critical
application data in a data center environment.
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Physical Elements of DAS
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CPU
Ÿ Motherboard
Ÿ Clustered group of processors
Ÿ Processor cards
Ÿ Complete system
Ÿ Internal
Ÿ External
Ÿ Hard disk(s)
Ÿ CD-ROM drive
Ÿ Optical drive
Ÿ Removable media
Ÿ Tape devices/tape library
Ÿ RAID/intelligent array(s)
Ÿ Portable media drives
Connectivity
Storage
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Benefits of DAS
• Ideal for local data provisioning
• Quick deployment for small environments
• Simple to deploy in simple configurations
• Reliability
• Low complexity
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Challenges in DAS
• Hosts must be directly connected
• Data availability
– Many single points of failure (i.e., bus, multiple path software,
host, application, etc.).
– There is no redundancy or fault tolerance for existing system.
– Inability to share data or unused resources with other hosts
simultaneously.
• Scalability is limited
– Number of connectivity ports to hosts
– Number of addressable disks
– Distance limitations
• Scheduled downtime planning and storage provisioning
necessary.
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Introduction (1/2)
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Users Shared the
Directories from
their Workstation
File Servers used as
central repository
Introduction of
NAS
Managing Data
security/Integrity ??
FS: Performance & Scalability?
PC: OS overhead?
Commodity Hardware: Meeting PSAR req. of growing Enterprise?
• NAS addressed the challenges of File Sharing & File Servers
High-performance, scalable
hardware, Specialized OS and
Protocol interfaces for file serving
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Introduction (2/2)
• NAS is a file-level shared networked storage that is capable of
providing data access to a heterogeneous group of clients.
– File System: Structure and logic rules used to manage groups of
information (files) and their names.
• NAS technology is now available for SMEs though it was
typically very high-end & expensive.
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Networked Environment of NAS (1/2)
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Clients
Application
Server
Print
Server NAS Device or Appliance/Filer
NAS Head Storage
NAS head can be remote or
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Networked Environment of NAS (2/2)
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Disks for File System A
Disks for File System B
NAS Device A
File System A
NAS Device B
File System B
Internal/External connectivity
to disks or arrays
Server A
File System A
Server B
File System B
Client 1
Client 2
Client 3
LAN
Linux
Windows
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General Purpose Servers vs. NAS
• NAS provides
– Real-time OS dedicated to file serving
– Open standard protocols
– Built-in native clustering for high availability
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Network
Operating System
I/O
File System
Print Drivers
Applications
General Purpose Server
(NT or Unix Server)
Network
Operating System
File System
Single Function Device
(NAS Server)
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Benefits of NAS (1/3)
• Supports global information access
– Enables greater file sharing, even over a long distance.
– Supports many-to-one or one-to-many configurations.
– Can share data across platforms.
• Improves efficiency through specialized OS, optimized for
file serving
– Eliminates bottlenecks encountered when accessing files from
central file server.
– Relieves general-purpose servers of many file management
operations, improving performance of those servers.
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• Centralizes storage
– Minimizes duplication on client workstations, reducing
management complexity and improving data protection.
• Simplifies management
– Leverages existing security infrastructure through standard
network protocols.
– Single point of management for multiple systems for multiple
data sets.
– Identifies data by file name and byte offsets, transfers file data
or file meta-data.
• Flexibility
– Works with many types of clients on both UNIX and Microsoft
Windows platforms using Industry standard protocols.
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• Scalable
– Due to its high performance, low latency design, enables NAS
to scale well and depending upon utilization profiles, address
many differing types of business applications.
• High availability
– Replication and recovery options
– Can safely centralize large amounts of user data behind a
single NAS device with redundant networking equipment to
provide maximum connectivity options.
– Clustering technology for failover in the event of filer failure
• Handles security, user authentication, and file locking in
conjunction with industry standard security schemas.
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NAS Device Components
• Examples of optimized OS based on Windows/UNIX/LINUX.
– DART (EMC’s Data Access in Real Time)
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NAS Device
Network Interface
Storage Interface
NAS Device OS
SCSI, FC, or ATA
CIFSNFS
IP Network
client
client
NFS
CIFS
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NAS File Service Protocols
• File Service Protocols allow users to share file data across
different operating environments & also provides
transparent migration from one OS to another.
• Common protocols
– NFS (for UNIX-based OS), developed by Sun
– CIFS (for Windows-based OS), developed by Microsoft.
• File system is mounted remotely using NFS or CIFS protocol
• Application I/O requests transparently transmit data to the
remote file system by the NFS/CIFS protocol. This is also
known as redirection.
• Utilizes data transport (TCP/IP) and media access protocols
• NAS device assumes responsibility for organizing block level
data (R/W) on disk and managing cache
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Challenges
• Speed
– Network latency and congestion
• Reliability
– Due to the large geographical coverage of enterprise networks
there are inherent possibilities for network failures, but with
redundancy planning these issues can be minimized.
– Centralized storage may become single points of failure
without remote mirroring or backup facilities.
• Scalability
– Although NAS devices can scale to terabytes of storage
capacity, once the capacity is exhausted the only way to
expand is to add additional devices. This can cause additional
problems.
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= Fibre Channel
Legend
SAN Switches
NT Server
IBM: AIX
HPUX servers
SUN: Solaris
Linux servers
SAN switches
Storage Array
SAN Switches
SAN Configuration (1/2)
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SAN Configuration (2/2)
• SAN is a block-level dedicated networked storage that
carries data between computer systems and storage devices
(disk arrays, tape libraries, and optical jukeboxes) via FC
Fabric topology.
• SANs can also support
– Disk mirroring
– Archival and retrieval of archived data
– Backup and restore
– Data migration from one storage device to another
– Data sharing among various servers.
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Networked Environment
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Client 2
Client 3
Client 1 Server A
Application A
Server B
Application B
Server C
Application C
Disks for Server A
Disks for Server B
Disks for Server C
SANLocal Area
Network
Disk Array
Fiber Channel
FC Switch
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Return to Slide #111

Components of SAN
• Components of SAN include
– Host Bus Adapter (HBA)
• Installed in a Server (including the device drivers needed) to
communicate within the SAN
– FC Switch/Hub
– Storage Array
– Management System
• Analyze and configure SAN components.
• SAN forms a communication infrastructure providing physical
connections & consists of a management software, which
organizes the connections, storage elements, and computer
systems so that data transfer is secure and robust.
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Nodes, Ports & Links
• Node are devices that are connected to the SAN using Ports
for purposes of requesting or supplying data (e.g. servers
and storage).
• A port has two connection points: transmit (Tx) link &
receive (Rx) link.
– Data traveling simultaneously through these links is referred to
as Full Duplex.
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Node
Port 0Port 0
Port 1Port 1
Port nPort n
Link
Port 0Port 0 Rx
Tx
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Benefits of SAN
• High bandwidth using FC.
• Resource Consolidation
– Centralized storage and management
• Scalability
– Up to 16 million devices
• Reliability
– Disk mirroring possible
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SAN vs. NAS
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Key Differences NAS SAN
Access Methods File access Disk block access
Access Medium Ethernet Fiber Channel
Architecture Decentralized Centralized
Transport Protocol Layer over TCP/IP SCSI/FC and SCSI/IP
Efficiency Less More
Sharing and Access Control Good Poor
Typical Applications Web Database
Typical Clients Workstations Database servers
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Storage System
• Storage is a technology which uses components and
recording media to retain digital data for the purpose of
future usage. It is a core function and fundamental
component of computers.
– The volatile technologies are referred to as memory and the
slow non-volatile (permanent) technologies are referred to as
Storage.
• The computer represents data using binary number system.
– Text, numbers, pictures, audio are converted into string of bits
or binary digits having value of 0 or 1.
• Measuring Storage in a Computer
– bytes, Kilobytes(KB), Megabytes(MB), Gigabytes(GB),
Terabytes(TB), etc.
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Types of Storage
• Primary Storage
– Primary storage is also known as memory, which is directly
accessible to the CPU.
– Examples: RAM and Cache memory.
• Secondary Storage
– Secondary storage is also referred to as external memory or
auxiliary storage and is the one which is not directly accessible
by the CPU.
– Examples: ROM, Flash memory, Floppy disks, magnetic tapes,
Optical devices like CD, DVD and also Zip drives.
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Hard Disk Drive (1/10)
• Most widely used storage device in Desktops and Laptops.
• External disks can be connected using interfaces like SCSI,
USB or eSATA.
• Disk Drive Components
– Platter
– Spindle
– Read and Write Head
– Actuator
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• Platter
– Hard Disk Assembly contains series of magnetic
coated disks called “platters” stacked one above
other within a sealed case.
• Number of platters on a drive is specific to a
particular drive.
• The drive’s capacity is determined by no. of platters,
amount of data stored per platter, and how
efficiently data is written to the platter.
– Data can be read/written from/on both surfaces of
a platter with drive heads.
– Data is stored in binary code (0s and 1s).
• It is encoded by polarizing magnetic areas, or
domains, on the disk surface.
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• Spindle
– Multiple platters are connected by a spindle to a motor which
rotates at a constant speed (several 1000 rpm) until power is
removed from the spindle motor.
• These speeds will increase as technologies improve, though there
is a physical limit to the extent to which they can improve.
– Many hard drive failures occur when the spindle motor fails.
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Spindle
Platters
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• Read/Write Head
– Most drives have two R/W heads per platter (one per surface).
– Data R/W is a magnetic process of detecting & changing
magnetic polarization on platter surface.
– Head Flying Height: Microscopic air gap between R/W heads
and the platter when the spindle rotates (R/W is in progress).
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• Read/Write Head (contd.)
– Landing Zone: A special area on the surface of platter near the
spindle where the R/W head rests when the spindle has
stopped its rotation.
• Landing zone is coated with a lubricant to reduce head/platter
friction. Logic on the disk drive ensures that the heads are moved
to the landing zone before they touch the surface.
– Head Crash: Drive malfunctioning may result in the R/W head
accidentally landing on the surface of the platter outside the
landing zone.
• Head crash generally results in data loss due to scratches on the
magnetic coating on the platter. The R/W head may also get
damaged.
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• Actuator
– An actuator is an electronic device controlled by a motor to
position the R/W heads at the location on the platter where
data needs to be read or written.
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Actuator
Spindle
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• Physical Disk Structures
– Actuator Arm Assembly
– Sectors & Tracks
– Cylinders
• Actuator Arm Assembly
– R/W heads for all of the platters in
the drive are attached to one
actuator arm assembly and move
across the platter simultaneously.
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Actuator
R/W Head
R/W Head
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• Tracks
– A track is a concentric ring in the platter
around the spindle which contains information.
Data is recorded in tracks.
– Tracks are numbered from the outer edge of
the platter, starting at track zero.
– Track density: No. of tracks on per unit length
of a platter.
– A track is divided into sectors.
• First PC hard disks had 17 sectors per track.
Today's hard disks can have a much larger no. of
sectors in a single track & thousands of tracks
on a platter, depending on the size of the drive.
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Sector
Track
Platter
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• Sectors
– Smallest individually-addressable unit of storage.
– Sectors typically hold 512 bytes of user data. Some disks can
be formatted with larger sectors.
– Capacity of Formatted vs. Unformatted Disk
• A formatting operation performed by the drive manufacturer
writes the track and sector structure on the platter.
• Once formatted, each sector can store user data as well as other
information (like sector no., head/platter no. & track no.). This
information aids the controller in locating data on the drive, but
it also takes up space on the disk.
• Capacity of Formatted disk is less compared to the capacity of an
unformatted disk. Drive manufacturers generally advertise the
formatted capacity.
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• Cylinders
– Set of identical tracks on both surfaces of
each of the drive’s platters.
– Often the location of drive heads are
referred to by cylinder no. rather than by
track no.
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Cylinder
Tracks, Cylinders and Sectors
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Disk Scheduling (1/6)
• Disk Scheduling is used to provide better solution to
minimize the access time required to R/W data to hard disk.
It is also used to minimize the seek time.
– Seek Time is the time required for the R/W head to reach tge
desired track from its current position.
• Algorithms
– FCFS (First Come First Serve)
– SSTF (Shortest Seek Time First)
– SCAN or Elevator
– C- SCAN (Circular SCAN)
– LOOK
– C-LOOK (Circular LOOK)
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• FCFS (First Come First Serve)
– Requests are addressed in the order they arrive in disk queue.
– Advantages:
• Every request gets a fair chance
• No indefinite postponement
– Disadvantages:
• Does not try to optimize seek time
• May not provide the best possible service
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• SSTF (Shortest Seek Time First)
– Seek time of every request is calculated in advance in queue
and the requests having shortest seek time are executed first.
• Note: The request near the disk arm will get executed first.
– Advantages:
• Average Response Time decreases
• Throughput increases
– Disadvantages:
• Overhead involved in calculating the seek time in advance.
• Can cause Starvation for a request if it has higher seek time as
compared to incoming requests with less seek time.
• High variance of response time as SSTF favors only some
requests.
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• SCAN or Elevator
– Disk arm moves in a particular direction & services the requests
coming in its path. After reaching the end of disk, it reverses its
direction & again services request arriving in its path.
• Note: The requests at the midrange are serviced more and those
arriving behind the disk arm will have to wait.
– Advantages:
• High throughput
• Low variance of response time
• Average response time
– Disadvantages:
• Long waiting time for requests for locations just visited by disk
arm
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• C-SCAN (Circular SCAN)
– Similar to SCAN, except that the disk arm moves inwards
servicing requests until it reaches the innermost cylinder; then
jumps to outside cylinder of the disk without servicing any
requests. Repeats this over and over.
– Advantages:
• Provides more uniform wait time compared to SCAN
• LOOK
– Similar to the SCAN, except that the disk arm goes to the last
request to be serviced in front of the head (in spite of going to
the end of disk) & then reverses its direction from there only.
– Note: LOOK prevents the extra delay which occurred due to
unnecessary traversal to the end of the disk.
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• C-LOOK
– Similar to C-SCAN, the disk arm goes only to the last request to
be serviced in front of the head (inspite of going to the end) &
then from there goes to the other end’s last request.
– C-LOOK prevents the extra delay which occurred due to
unnecessary traversal to the end of the disk.
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RAID
• Disk Array or RAID (Redundant Array of Independent Disks)
technology increases the performance and reliability of data
storage by presenting the combination of two or more
physical drives as a single logical unit (single hard drive).
– Multiple disks increases MTBF.
• MTBF is typically in 1000s or tens of thousands of hours between
failures. Example, a HDD may have a MTBF of 300,000 hours.
• Enables storage of same data (redundantly) in multiple hard
disks (all RAID levels do not provide redundancy).
– I/O operations can overlap in a balanced way, improving
performance.
– Storing data redundantly also increases fault tolerance.
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RAID Functions
• Striping: Process in which consecutive logical bytes of data
are stored as blocks in the consecutive physical disks which
forms the array.
• Mirroring: Process in which the data is written to the same
block on two or more physical disks in the array.
• Parity Calculation: Redundancy information is calculated for
each piece of data stored.
– If no. of disks in the RAID array is N, then
• (N-1) consecutive blocks are used for storing data blocks &
• Nth block is used for storing the parity.
– If a drive fails, the missing data can be reconstructed from the
remaining data & parity data. Error checking can slow down
the system because data from several locations must be read
and compared.
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RAID Types (1/9)
• RAID 0 (Data Striping with no Parity)
• RAID 1 (Data Mirroring)
• RAID 1+0 or RAID 10 (Stripe of Mirrors)
• RAID 0+1 or RAID 01 (Mirror of Stripes)
• RAID 4 (Striping with dedicated parity)
• RAID 5 (Striped Data and Parity)
• RAID 6 (Striped Data with Dual Parity)
• Extended RAID (RAID 5E, RAID 5EE)
• Less Popular RAID types (RAID 2, RAID 3)
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RAID Types (2/9)
• RAID 0 (Block-level Striping with no Parity)
– RAID 0 requires a minimum of two HDDs.
• Total capacity = No. of discs x Capacity of the “smallest” disk.
– E.g. If we have two HDDs – 250GB and 500GB, the total size of the
array will be equal to 500GB.
– Advantages: Increase in performance due to parallelism in the
read and write process.
– Disadvantage: No redundancy.
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RAID Types (3/9)
• RAID 1 (Disk Mirroring)
– RAID 1 requires a minimum of two or more
HDDs.
• Total storage = Capacity of the smallest disk.
– E.g. In the case of an array composed of 3
discs – 250GB, 500GB and 1TB, the usable
space will be equal to 250GB.
– Advantages:
• Good performance in Read operation as
data is read parallel from several disks,
Tolerance from Disk failure.
– Disadvantage:
• Slow write process as multiple writes are
required, Cost is doubled, Not good for data
loss due to viruses or human factors.
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RAID Types (4/9)
• RAID 1+0 or RAID 10 (Stripe of Mirrors)
– Combination of RAID 1 (Mirroring) and RAID 0 (Data Stripping)
in which mirroring is on inside and the data stripping happens
on the outside.
– Advantage: Good performance in Reads & improvised write
performance when compared to RAID 1.
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RAID Types (5/9)
• RAID 0+1 or RAID 01 (Mirror of Stripes)
– Combination of RAID 0 (Data Stripping) and RAID 1 (Mirroring)
in which data stripping happens on inside and mirroring
happens on the outside.
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RAID Types (6/9)
• RAID 4 (Striping with dedicated Parity)
– Data is stored across (N-1) disks and Nth disk acts as dedicated
Parity Drive which stores the parity information. Requires a
minimum of 3 HDDs for its configuration.
• When adding one drive for parity it would be able to rebuild the
missing data in case of any drive failure.
– Used with really large files with sequential read & write data.
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RAID Types (7/9)
• RAID 5 (Striped Data and Parity)
– Identical to RAID 4, but parity is striped across multiple drives
in the array. Requires a minimum of 3 HDDs for its
configuration.
– Advantage: Good read performance due to the parallelism like
RAID 0, Good write performance due to the striping of parity
bits.
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RAID Types (8/9)
• RAID 6 (Striping with Dual Parity)
– Data is striped with dual parity across drives in the array.
– Advantages: Two times more resistant than RAID 5, speed of
whole system is higher than in the case of a single disk.
– RAID 6 is an almost ideal solution if cost of implementation is
not taken into account.
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RAID Types (9/9)
• Extended RAID
– RAID 5E (RAID 5 with built-in spare drive)
– RAID 5EE (RAID 5E with distributed spare)
• Less Popular RAID types
– RAID 2 (Bit-level Stripping with dedicated Hamming Code
Parity)
• Good solution in area of data security. In case of HDD failure – no
matter if it was the disk with data or the Hamming code – any
part of the array may be reconstructed by the other disks used.
– RAID 3 (Byte-level Stripping with dedicated Byte-level
checksum parity)
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Optical Storage (1/2)
• One of the low-cost and reliable storage media used in
personal computers for data backup or archiving.
• Capacity and speed is low compared with HDD & Tape drives.
• Popular Types include:
– Compact Disk(CD), Digital versatile disk(DVD), Blue-ray disk(BD)
• An optical disc is designed to support one of the three
possible recording types:
– Read-only (e.g. CD and CD-ROM)
– Recordable (write-once, e.g. CD-R), or
– Re-recordable (rewritable, e.g. CD-RW).
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Optical Storage (2/2)
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Pits and Land
• Surface of a CD is made of a
polycarbonate layer with molded
spiral tracks on the top.
• Pits & Land
– Data is stored as a series of minute
grooves known as ‘pits’ encoded on
these spiral tracks.
– The areas between the ‘pits’ are
known as ‘lands’.
• Size of a pit & Track spacing may
vary (hence the Capacity) among
Optical devices.
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R/W Process (1/2)
• While CDs are played they are made to rotate around for
R/W.
• CD burning (Write) process
– Powerful “write laser” creates a series of pits as per the data
(binary values) on the surface.
• CD reading process
– A less powerful “read laser” bounces the light beam on the
surface and detects the pits and lands, thus creating actual
data in binary form.
• Each change between pit to land or vice versa is translated as
zero
• No change (pit to pit or land to land) is translated as one.
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R/W Process (2/2)
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Solid State Drives
• Solid-state storage devices use IC assemblies as memory to
store data.
• Solid state drives (SSDs) do not contain any moving parts like
the magnetic drives.
• Also known as flash memory, thumb drives, USB flash drives,
Memory Stick, Secure digital cards.
• SSDs are relatively expensive when compared to the other
types for their low capacity, but are very convenient for
backing up the data.
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Network Storage
• Data is stored or backed-up on the remote storage provided
by the organization or application network servers and can
be accessed from a remote location.
• Remote operations are facilitated over Internet.
• Storage is made possible in a range of devices.
• Note: Refer Topics-2,3,4
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Comparison
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Hubs (1/2)
• Hub is a Physical Layer device used a central point of
connection among media segments. Cables from network
devices plug in to its ports.
• Hubs cannot filter data. Data packets are sent to all
connected devices/computers & do not have intelligence to
find out best path for data packets.
• Types of Hubs
– Passive hub (Connector)
• Connects networking cables coming from different branches. The
signal pass through a hub without regeneration or amplification.
– Active hubs (Multiport repeaters)
• Connects networking cables coming from different branches and
regenerate or amplify the signal before they are retransmitted.
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Hubs (2/2)
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Bridge (1/2)
• It works at the data-link (physical network) level of a
network. Hence it is capable of checking the PHYSICAL/MAC
addresses (source and destination) contained in the frame.
• A Bridge connects a LAN to another LAN that uses the same
protocol.
• A bridge table used in filtering decisions.
• Unlike a Hub, a Bridge checks the destination address of a
packet, maps address to ports (using bridge table) and
decide if the frame should be forwarded or dropped.
– It restricts transmission (Dropping) on other LAN segment if
destination is not found.
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Bridge (2/2)
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Switch
• Switches are layer 2 (based on MAC Address) devices. It may
support layer 3 (based on IP address) connectivity depending
on the type of switch (Intelligent Switch).
• Switches can perform error checking before forwarding data
– Can be very efficient by not forwarding packets with error &
forwarding good packets selectively to correct devices only.
• A switch when compared to bridge has multiple ports.
• Usually large networks use switches instead of hubs to
connect computers within the same subnet.
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Router
• Router is a Layer-3 (Network Layer) device capable of routing
packets based on their logical or IP addresses (host-to-host
addressing).
• A router normally connects LANs and WANs in the Internet.
• Uses Dynamic routing table for making decision about the
route.
– Routing tables are normally updated using routing protocols.
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Router vs. Bridge (1/2)
• Router works with logical address while bridge works with
physical/ MAC address
• Message Size
– Routers can perform fragmentation on packets and thus
handle different packet sizes.
– Bridges cannot do fragmentation and should not forward a
frame which is too big for the next LAN.
• Forwarding
– Routers forward a message to a specific destination.
– Bridges forward a message to an outgoing network.
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Router vs. Bridge (2/2)
• Priority
– Routers can treat packets according to priorities
– Bridges treat all packets equally.
• Error Rate
– Network layers have error-checking algorithms that examines
each received packet.
– The MAC layer provides a very low undetected bit error rate.
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Gateway
• Gateway can be used to connect two networks together that
may work upon different networking models (protocols and
topologies).
• Gateways are also called protocol converters and can
operate at any network layer.
• Gateways are generally more complex than switch or router.
• They basically works as the messenger agents that take data
from one system, interpret it, and transfer it to another
system.
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FC Ports
Port Full Name Port Function
N-port network port or node port Node port used to connect a node to a FC switch
F-port fabric port Switch port used to connect the FC fabric to a node
L-port loop port Node port used to connect a node to a FC loop
NL-port network + loop port Node port which connects to both loops and switches
FL-port fabric + loop port Switch port which connects to both loops and switches
E-port extender port Used to cascade FC switches together
G-port general port
General purpose port which can be configured to emulate
other port types
EX_port external port
Connection between a FC router & FC switch. On the
switch side, it looks like a normal E-port, but on the router
side, it is a EX_port
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• A FC port is a hardware pathway into/out of a node/switch
that performs data communications over an Fiber Channel.
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Point to Point
• Enables direct connection between nodes allowing two-way
data communication between them.
• Offers little connectivity and scalability.
• Used with DAS environment.
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FC – AL (1/5)
• FC-AL topology is used where interconnection of storage
devices is needed & where multiple node connections
require high bandwidth.
• FC-AL technology eliminates the expensive FC switches and
allows several servers and storage devices to be connected.
• Can connect up to 127 devices with a port attached to fabric.
– Only one port can transmit data at a time.
• The devices use an Arbitration signal to choose the port. After
port selection a device can use the FC .
• Has Serial Architecture compatible with SCSI.
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FC – AL (2/5)
• Direct Cabled Loop
– FC-AL topology is similar to a IBM Token Ring network.
– All devices share the same bandwidth in loop.
– Data passed using one-way loop technique.
– Token is used to prevent data from colliding when two or more
streams are sent at the same time.
– If a port malfunctions in the loop, all ports stop working.
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FC – AL (3/5)
• Loop Hub
– A hub (or) concentrator makes cabling easier.
– The devices are connected through Hubs for reliability and
ease of management.
• Can detect and bypass a bad device or segment of broken fiber
so it would not bring down the whole network.
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FC – AL (4/5)
• FC-AL Types
– Private loops
• Loops are not connected to the Fabric.
• Nodes in the loop cannot access the nodes that are not part of
the loop.
– Public loops
• Loops are connected to the Fabric through one FL Port
• Nodes are accessible to other nodes that are not part of the loop.
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FC – AL (5/5)
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FL_Port: Connects to
FC Loop & Switch
NL_Port: Connects
to FC Loop & Switch
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FC – Switched Fabric (1/8)
• FC Switched Fabric network topology is used to connect
network nodes/devices with each other using one or more
FC switches.
• Offers best scalability of the other FC topologies.
– Traffic is spread across multiple physical links.
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• SAN FC Switched Fabric is used to connect workstations and
servers to the storage device in a SAN.
– FC switching technology is used in a SAN Fabric to enable any-
server to any-storage device connectivity.
– Environment-1 (click to Refer Slide 43)
– Environment-2 (Increased reliability)
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• Switched Fabric can be segmented to control visibility among
various devices/ports in the Fabric.
• Segmentation methods
– Zoning
– LUN Masking
• Zoning
– Process of segmenting switched fabric into various zones.
– Zone Members: Ports and devices in a zone
• Ports that are members of a zone can communicate with each
other, but they are isolated from ports in other zones.
• Devices can belong to more than one zone.
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• Why Zoning?
– Segregate different environments whose file-systems might be
incompatible with each other. E.g. Windows, Unix/Linux, AIX,
Mac
– Segregate storage-intensive environments (E.g. Windows) from
other environments that make lesser memory/storage
demands.
– Segregate a server cluster that stores confidential information
from unauthorized access.
• Implementation methods of Zoning
– Hardware Zoning
– Software Zoning
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• Software Zoning (Simple Name Server based)
– Based on node/port WWN or WWPN of the zone members to
be included. Software Zoning creates symbolic names for the
zones and zone members.
• Device’s physical connectivity to a port is not considered for
defining zones.
– The entire zone continues to operate even if the devices are
shifted to a different port.
– Maintains a table of storage devices that are accessible to each
member of the zone.
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• Hardware Zoning (Port-based)
– Nodes/Devices are connected to the ports. Physical ports can
be assigned to one zone (or) shared with multiple zones
(shared) at the same time.
– The entire zone ceases to operate even if one device is shifted
to a different port.
– More secure than Software Zoning.
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• Zoning in SAN
– A zone is a logical grouping of ports to form a virtual private
storage network.
– Zone Set
• Zones that belong to a single SAN.
• Can be activated or deactivated as a single entity across all
switches in the fabric.
• Contains one or more zones, and a zone can be a member of
more than one zone set.
– Zone Alias
• Meaningful names assigned to devices.
• An alias can also be a collection/group of devices that are
managed together to make zoning easier.
• A zone alias can be added to one or more zones.
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• LUN Masking
– A more effective method of segmenting a SAN based on the
Logical Unit Number (LUN) assigned to each storage device or
partition that a storage device can support.
– Every node on a SAN can access the storage device/partition
by using these LUNs.
– A server or set of servers can request to access a storage
device or partition by specifying the LUN. The storage device
checks its access list and grants access if the server has proper
rights.
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Storage Virtualization (1/5)
• Process of presenting a logical view of physical storage
resources to hosts.
– Logical storage appears and behaves as physical storage
directly connected to host.
• Storage system uses virtualization concepts which enables
better functionality and advanced features within and across
storage systems.
• Hides the complexity of the SAN by pooling together
multiple storage devices to appear as a single storage device.
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• Categories
– Host based
• The virtualization layer is provided by a server and presents a
single drive for the applications.
• The host based storage virtualization depends on the software at
the server often at the OS level.
– Appliance based
• In the Appliance based virtualization a hardware appliance which
is used sits on the storage network.
– Network based
• Similar to the appliance based except that it works at the
switching level.
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• Types
– Block Virtualization
• The abstraction (separation) of logical storage (partition) from
the physical storage so that the partition can be accessed without
regard to the physical storage.
– File Virtualization
• File virtualization eliminates the dependencies between the data
accessed at the file level and the physical location where the files
are stored.
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• Advantages
– Improvised storage management in an IT environment
– Better availability
– Better storage utilization
– Less energy usage
– Increase in loading and backup speed
– Cost effective, no need to purchase additional software and
hardware
• Disadvantages
– Uses a network system which is more complicated
– Failure in any one of the system fails the entire setup
– The entire network is compromised if any server is infected or
breached.
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Peep into the next Module
• System Overview
– Server Technology
– Operating System
– Virtualization
– Server Deployment
– Server Availability Concepts & Techniques
– Server Workload
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Storage overview

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Storage overview