Secondary Storage - General Knowledge

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It is a brief review of secondary storage technologies to find that how we can use it better in our systems.

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Secondary Storage - General Knowledge

  1. 1. Secondary Storage A BRIEF REVIEW OF HARD DISK DRIVES AND STORAGE TECHNOLOGIES
  2. 2. Internal Structure Medical Infromation Management - Autumn 2013 2
  3. 3. Internal Structure (Cont.) • Head flies above platters • Platter are divided into circular tracks and tracks which are subdivided into sectors. The set of tracks at one arm position make cylinder. • Logical blocks, the smallest unit of transfer (512 bytes) that maps to the sectors. Medical Infromation Management - Autumn 2013 3
  4. 4. Internal Structure (Speed) • Disk speed has two parts: • Transfer Rate, the rate at each data flow between the drive and computer. • • Efficient Transfer Rate Position Time (Random-Access Time), • • Seek time, the time necessary to move disk arm to the desired cylinder. Rotational Latency, time necessary for the desired sector to rotate to disk head. Medical Infromation Management - Autumn 2013 4
  5. 5. Internal Structure (Head Crash - Connection) • Head Crash, head may contact the surface • I/O bus connects Disk Drive to the computer. EIDE • ATA, PATA, SATA • USB • FC • SCSI • FireWire! (Developed by Apple, IEEE 1934 standard) (400 Mbps) • • A disk controller is built into each disk drive that has a cache ... Medical Infromation Management - Autumn 2013 5
  6. 6. Medical Infromation Management - Autumn 2013 6
  7. 7. Magnetic Tapes • Early secondary storages with very slow access time (1000 times slower than HDD) • Can be used for back up or non-frequently used data. Medical Infromation Management - Autumn 2013 7
  8. 8. Disk Attachment • Host-Attachment Storage (via I/O) common for small systems. • Network-Attach Storage, remote host in a distributed file system • • Remote-procedure call interface (NFS for UNIX, CIFS for windows) NAS is implemented as a RAID (redundant array of independent disks) array with software that implements RPC interface. Medical Infromation Management - Autumn 2013 8
  9. 9. NAS Medical Infromation Management - Autumn 2013 9
  10. 10. Server Medical Infromation Management - Autumn 2013 10
  11. 11. Storage Area Network • Drawback in NAS: Storage I/O operations consume Bandwith Medical Infromation Management - Autumn 2013 11
  12. 12. SAN • Oracle • Google • Hp • … Medical Infromation Management - Autumn 2013 12
  13. 13. RAID • Disks get smaller and cheaper • Redundant Arrays of Independent (not completely) Disks • Inexpensive -> Independent • Increasing read and write rate (Parallel) - increase the throughput (load balancing) / reduce response time of large accesses • Increasing Reliability (Redundant) – Mirroring • RAID levels (Redundancy to Striping) Medical Infromation Management - Autumn 2013 13
  14. 14. RAID Levels – 0 • Nothing Medical Infromation Management - Autumn 2013 14
  15. 15. RAID Levels – 1 • Mirroring Medical Infromation Management - Autumn 2013 15
  16. 16. RAID Levels – 2 • Parity bits - ECC Medical Infromation Management - Autumn 2013 16
  17. 17. RAID Levels – 3 • Parity bits • Less disks • Much Speed • fewer I/O • Dedicated Parity Hardware Medical Infromation Management - Autumn 2013 17
  18. 18. RAID Levels – 4 • Like 3 but blocks in each disk • Higher level of I/O rate Medical Infromation Management - Autumn 2013 18
  19. 19. RAID Levels – 5 • Spreading the parity blocks • Safer - Most Common Medical Infromation Management - Autumn 2013 19
  20. 20. RAID Levels – 6 • Like 5, Parity + Reed Solomon ECC Code Medical Infromation Management - Autumn 2013 20
  21. 21. RAID Levels – 0+1 , 1+0 Medical Infromation Management - Autumn 2013 21
  22. 22. Choosing a RAID Level • Continues supply of data is needed • Rebuilding is easiest in RAID level 1 • Level 0 for high performance where data loss is not so important • Level 1+0 and 0+1 for both Performance and reliability (ex. Small Databases) • Level 5 can be used instead of 1 • Level 6 is not supported commonly, but it should be more reliable that level 5 Medical Infromation Management - Autumn 2013 22
  23. 23. • How many disks should be in a given RAID set? • More disks, More Data-Transfer Rate, More Expensive • How many bits should be protected by each parity bit? WHAT SHOULD WE THINK ABOUT? • Less bits each parity, More Chance to Modify the Failure, More Overhead Medical Infromation Management - Autumn 2013 23
  24. 24. SSD VS. HDD Solid State Drive Hard Disk Drive Medical Infromation Management - Autumn 2013 24
  25. 25. Medical Infromation Management - Autumn 2013 25

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