Advanced Storage Area Network
- 1. Storage Area Network Module 2 (2nd Part) Presented By- Soumee Maschatak 1EW18SCS07 MTECH(SCS)
- 2. Contents 1. Local File Systems 2. Network File system and file servers 3. Shared disk file systems 4. Case Study: General Parallel File System
- 3. Local File System 1. File systems and databases – File systems and volume manager provide their services to numerous applications with various load profiles. This means that they are generic applications; their performance is not generally optimized for a specific application. 2. Journaling – It is a mechanism that guarantees the consistency of the file system even after a system crash. After a system crash, the file system only has to run through the end of the log file in order to recreate the consistency of the file system. 3. Snapshots – It represents the same function as the instant copies function that is familiar from disk subsystems. Snapshots freezes the state of a file system at a given point in time.
- 4. 4. Volume Manager – It is an intermediate layer within the operating system between the file system or the database and the actual hard disks. The most important basic function of the volume manager is to aggregate several hard disks to form a large virtual hard and make just this virtual hard disk visible to higher layers. Local File System
- 5. Network File Systems and File Servers • Network file systems are the natural extension of local file systems. End users and applications can access directories and files that are physically located on a different computer over a network file system. • File servers are so important in Modern IT environments that preconfigured file servers, called Network Attached Storage (NAS), have emerged as a separate product category. • With the aid of network file systems, end users and applications can work on a common data set from various computers. • FTP servers are an important means of distributing freely available software and freely available documents. • Unlike network file systems, access to FTP servers is clearly visible to the end user.
- 6. Network Attached Storage (NAS) • It is the name for preconfigured file servers. • They consists of one or more internal servers, preconfigured disk capacity and usually a stripped-down or special operating system. • NAS servers are specially developed for file sharing. This has 2 advantages – • NAS operating systems can be better optimised than generic operating system • NAS servers provide plug and play file systems, ie, connect – power up – use. • NAS servers are very scalable. • One disadvantage of NAS servers is the unclear upgrade path. The upgrade options available are those offered by the manufacturer of the NAS server.
- 8. Performance Bottlenecks in file servers • The NAS servers and NAS gateways as well as classical file servers provide their storage capacity via conventional network file systems. • I/O intensive databases draw their storage from disk subsystems rather than file servers. • The NAS server’s operating system loads the file into the main memory from the hard disk via the SCSI bus, the PCI bus and the system bus, only to forward it from there to the network card via the system bus and the PCI bus. • If the load on a file server is high enough, its buses can thus become a performance bottleneck. • Every single copying operation increases the latency of the communication, the load on the CPU due to costly process changes between application processes and the kernel processes, and the load on the system bus between CPU and main memory.
- 9. Shared disk file system • The greatest performance limitations of NAS servers and self configured file servers is that each file must pass through the internal bus of the file servers twice before the files arrive at the computer where they are required. • The I/O bottleneck in the file server can be circumvented if all clients fetch the files from the disk directly via the storage network. • The shared file system can deal with this problem. • The shared disk file system must synchronize write access in addition to the function of the local file system. • The great advantage of the shared disk file system is that the computers accessing files and the storage devices communicates with each other directly.
- 10. Figure: Shared Disk File system
- 11. Case Study: General Parallel File System