![STORAGE MEDIUMS AND FRAGMENTATION 6
References
Englander, Irv. (2014-01-21). The Architecture of Computer Hardware and System Software: An
Information Technology Approach, 5th Edition. [VitalSource Bookshelf Online].
Retrieved from https://kaplan.vitalsource.com/#/books/9781118803127/
Evett, M (2015). Disk Allocation. retrieved May 22 2016, from YouTube Web Site:
https://www.youtube.com/watch?v=DWG6tO2EbjI
Microsoft, (2016). Description of the exFAT file system driver update package. retrieved May 23
2016, from Microsoft Web Site: https://support.microsoft.com/en-us/kb/955704
LeGault, L (2009). HFS+: The Mac OS X File System. retrieved May 23 2016, from Dep. of
Computer Science University of Wisconsin-Madison Web Site:
http://pages.cs.wisc.edu/~legault/miniproj-736.pdf
Rouse, M (2013). LTFS (Linear Tape File System). retrieved May 23 2016, from TechTarget
Web Site: http://searchdatabackup.techtarget.com/definition/LTFS-Linear-Tape-File-
System
IBM, (2010). Linear Tape File System (LTFS) Format Specification. retrieved May 23 2016,
from IBM Web Site: http://www-
01.ibm.com/support/docview.wss?uid=ssg1S7003166&aid=3
Indika, (2011). Difference Between Partition and Volume. retrieved May 24 2016, from
Difference Between Web Site: http://www.differencebetween.com/difference-between-
partition-and-vs-volume/
Dittrich, J (2013). 14.113 Hard Disks, Sectors, Zone Bit Recording, Sectors vs Blocks, CHS,
LBA, Sparing. retrieved May 24 2016, from YouTube Web Site:
https://www.youtube.com/watch?v=Cj8-WNjaGuM](https://image.slidesharecdn.com/ef171cc0-a322-4c24-8f04-f575c04e60b2-160622110343/85/Storage-Mediums-and-Fragmentation-6-320.jpg)
Storage Mediums and Fragmentation
- 1. Running head: STORAGE MEDIUMS AND FRAGMENTATION 1 Storage Mediums and Fragmentation Larry Reid Kaplan University IT332-01 Principles of Information Systems Architecture
- 2. STORAGE MEDIUMS AND FRAGMENTATION 2 Storage Mediums and Fragmentation There are several types of storage mediums and each of those mediums needs a file system to be useful. A lot of file systems suffer from the effects of fragmentation and some storage mediums become slow overtime needing to be defragmented. Sometimes it’s difficult to wrap our heads around concepts like this but this article is meant to make it as painless as possible to grasp these concepts and come to an understanding. what are file system allocation methods? A file system is what is used on a storage device to manage, maintain, and organize all of the data on it. File systems are things such as the New Technology File System (NTFS) used by Windows which stores data contiguously and uses indexing allocation, the File Allocation Table 32 (FAT32) and extended FAT (exFAT) which both use the File Allocation Table with linking, the Hierarchical File System Plus (HFS+) used by Apple which is extent-based allocation with indexing, and the Linear Tape File System (LTFS) developed by IBM for tape drives which also has extent-based allocation with indexing. Are you wondering what file system allocation methods are still? Well they are what explain how blocks are divided up and distributed each time a file is saved, each allocation method has a different way of defining how addresses to blocks are stored, some file systems only use one type of allocation method and others take the best from multiple methods and put them together. File systems are rules or a blueprint that the operating system follows in order to write, read, organize, and manage files all of which use some type of table with addresses to sectors and blocks, some keep track of how many blocks the file takes up, and others may be links to a block and then to another until they get to one that doesn’t have a link, which means the whole file has been found. Now let’s go over the different types of allocation. Contiguous allocation is method used to store data in a sequential set of blocks. When you save a file using this allocation method,
- 3. STORAGE MEDIUMS AND FRAGMENTATION 3 your file system has to figure out how many blocks are needed to store the file, and it then has to find free space on the disk with the amount of blocks needed, if it can’t find the space needed then it will fragment the file and place it in two or more sets of contiguous blocks. Using this method is the fastest way to access files for Hard Disk Drives (HDD) since the head does not have to move all over the disk to find all of the blocks that a file is stored on (Evett, 2015). Non-Contiguous allocation doesn’t care about allocating sequential blocks, they can be all over the disk and the files will have links to the next block that comprises more of the file until the last block which doesn’t contain a link, is reached, or it may store the file block locations in a master list. Non-Contiguous allocation does not have external fragmentation but does contain internal fragmentation (Englander, 2014). Indexed allocation uses index tables to store all the block addresses for each file. Each file gets its own index table typically stored in the first block allocated to the file. Additionally, there is a file management system that is used to maintain a directory that houses information about the files that can include attributes, the link locations, the pointer to the file, file name, etc. Whey a file is opened the operating system will store the files index table, that houses the links to all of the files blocks, in memory making it extremely fast to do random accesses to the file and also very efficient with memory usage. Typically, this is a non-contiguous allocation method but Windows NTFS allocates contiguous blocks as much as possible to save additional memory (Englander, 2014). Tape allocation is simpler than disk allocation. This is meant more for sequential reads and not really feasible for random access. Tape drives can be compacted, similar to defragmented, but it’s usually not worth the work, it would be easier to copy the data to another tape. The Linear Tape File System is a great method to use for storing files on a tape drive, using extent-based allocation along with indexing it allows the tape to almost act like a hard drive,
- 4. STORAGE MEDIUMS AND FRAGMENTATION 4 allowing for random read access. Though if the files need to be accessed more often, it would be more efficient to move or copy the files to a disk drive. Tape drives are better to be used for daily, weekly, or monthly backups (Englander, 2014). Disk allocation and storage allocation has to do with how a disk is broken up into zones, sectors, and blocks. So disks contain zones which are the tracks that contain the same number of blocks as adjacent tracks, so as you move closer to the center of the disk the zones change. Next we have sectors which are a section, shaped like a pie slice, that contain blocks, and blocks are 4 or 5 kilobyte sections on the disk. There are also OS blocks that are described by the operating system, one block for the OS can contain multiple disk blocks. What happens in disk allocation is the contiguous, non-contiguous, or whatever allocation method you are using, will allocate these blocks to the free disk space manager on the operating system and the OS will use the free disk space manager to allocate the disk blocks for storage (Dittrich, 2013). Partitions are divisions created within a disk, you can have between one and three primary partitions and one additional extended partition on a single simple disk volume. An extended partition can have several logical partitions created within it, which is how we can get around the four partition rule on hard disks. Additionally, we can create a dynamic disk which allows us to create several logical volumes which are generally the same as a partition but instead of the space residing on a single disk the logical volume can span across multiple disks. A physical volume refers to a physical hard disk in its entirety (Indika, 2011). Fragmentation can be broken up into two types, internal and external. Internal fragmentation is the space reserved by the file system to store index tables, FAT tables, and any other unused space that is set aside within a file, such as the reserved space for file expansion. External fragmentation refers to how a file is saved to the disk blocks. If a file must be broken up across the disk to be saved and is not saved in a contiguous manner, then it is considered
- 5. STORAGE MEDIUMS AND FRAGMENTATION 5 fragmented and the disk heads have to move, possibly, several times to write or read the file creating slower file read/write times. Defragmentation takes all of the broken up non-contiguous files and puts them in as much of a contiguous order as it can and then compresses all of the files together to fill in all of the little blocks of free space between files, which were created from deleting files. Defragmentation is used to make it easier for the disk heads to find files, and speeds up read/write operations that were slow because of fragmentation. The table below displays several different storage mediums, file systems, allocation methods, and various attributes about each of them. NTSF FAT32 exFAT HFS+ LTFS Can Produce Fragmentation Issues/Problems Contiguous Allocation No No No No No Yes Fragmentation, finding space for files, knowing file size, needs to compress files Linked Allocation No No No No No No Files can be scattered everywhere, uses links stored with each block and if one block loses its link the whole file is lost, not efficient Indexed Allocation Yes -with contiguous block allocation No No No No Yes Internal fragmentation is bad because of allocating index tables for each file, Index tables can create wasted space File Allocation Table (FAT) No Yes -Uses links at each file but has all links stored in fat table Yes -with contiguous block allocation No No No Not really recommended for running full operating systems on, better for embeded systems, small devices, and removable storage Extent-Based Allocation No No No Yes -with indexing Yes -with indexing Yes Suffers from both internal and external fragmentation Has Journaling Feature Yes No No No - but it can be turned on through the command line No N/A N/A Max Volume Size 16TB 2TB 64ZB - Recommended Max is 512TB 8EB 2.5TB N/A N/A Max Single File Size Read/Write 16TB 4GB 64ZB 8EB 2.5TB N/A N/A Allocation Unit Sizes 4096b - 64KB 512b - 4KB 16KB - 32MB 4096b - 64KB 16KB - 256KB N/A N/A Can Produce Fragmentation Yes -but its decreased with larger allocation unit sizes when formatting No Yes -but fragmentation does not cause as many issues unless your using an HDD. Yes Yes -internal fragmentation only, LTFS cannot be defragmented, unless it is reformated N/A N/A Flash Drive Yes Yes Yes Yes No Yes -very little effect on solid state storage Low maximum write cycles, HDD Yes Yes Yes Yes No Yes -slows file read/write speed over time, needs to be defragmented Uses physical heads and spinning disk, fragmentation can slow performance a lot SSD Yes Yes Yes Yes No Yes -very little effect on solid state storage SSD's offer very fast access but have a relatively short lifespan and are very expensive SD Card Yes Yes Yes Yes No Yes -very little effect on solid state storage Limited on write cycles, slow read/write speeds Tape Drive No No No No Yes -lets users navigate and interact like its a hard disk drive No Cannot be accesed randomly, though they can be very fast and easy to use for backups Windows Compatible Yes Yes -but optomize for quich removal option needs to be turned off to format FAT32 drives Yes Read Only Yes need special software and hardware N/A N/A Mac Compatable Read Only Yes Yes Yes Yes need special software and hardware N/A N/A
- 6. STORAGE MEDIUMS AND FRAGMENTATION 6 References Englander, Irv. (2014-01-21). The Architecture of Computer Hardware and System Software: An Information Technology Approach, 5th Edition. [VitalSource Bookshelf Online]. Retrieved from https://kaplan.vitalsource.com/#/books/9781118803127/ Evett, M (2015). Disk Allocation. retrieved May 22 2016, from YouTube Web Site: https://www.youtube.com/watch?v=DWG6tO2EbjI Microsoft, (2016). Description of the exFAT file system driver update package. retrieved May 23 2016, from Microsoft Web Site: https://support.microsoft.com/en-us/kb/955704 LeGault, L (2009). HFS+: The Mac OS X File System. retrieved May 23 2016, from Dep. of Computer Science University of Wisconsin-Madison Web Site: http://pages.cs.wisc.edu/~legault/miniproj-736.pdf Rouse, M (2013). LTFS (Linear Tape File System). retrieved May 23 2016, from TechTarget Web Site: http://searchdatabackup.techtarget.com/definition/LTFS-Linear-Tape-File- System IBM, (2010). Linear Tape File System (LTFS) Format Specification. retrieved May 23 2016, from IBM Web Site: http://www- 01.ibm.com/support/docview.wss?uid=ssg1S7003166&aid=3 Indika, (2011). Difference Between Partition and Volume. retrieved May 24 2016, from Difference Between Web Site: http://www.differencebetween.com/difference-between- partition-and-vs-volume/ Dittrich, J (2013). 14.113 Hard Disks, Sectors, Zone Bit Recording, Sectors vs Blocks, CHS, LBA, Sparing. retrieved May 24 2016, from YouTube Web Site: https://www.youtube.com/watch?v=Cj8-WNjaGuM