Raid 1 3

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Raid 1 3

  1. 1. Topic RAID Redundant Array Independent Disk
  2. 2. Raid History
  3. 3. S.L.E.D. Single Large Expensive Disks Single drive used to store data.  Capacity: good Problem: Data cant be read and write quickly  If SLED fail then all data loss. 
  4. 4. Raid
  5. 5. RAID Overview: The heart of the RAID storage system is controller card. The task of the controller card is to Manage Individual Hard Disk Drives Provide a Logical Array Configuration Perform Redundant or Fault Tolerant Operations
  6. 6. Raid
  7. 7. Patented 1987 Built in 1989 Updated several times That’s all I could find. Until I made these updates….
  8. 8. RAID RAID: Redundant Arrays of Independent Disks Hence, the I in RAID now stands for“independent”instead of “inexpensive”. RAID:Multiple disk drives provides reliability via redundancy. commonly used to address the performance and reliability issues.
  9. 9. Redundancy: Mirroring Duplicate every disk Gives good error recovery Data stripping A method of concatenating multiple drives into one logical storage unit. the data is split into different parts. Parity: Splitting data onto blocks with the help of XOR operation
  10. 10. What exactly is a RAID? RAID is basically drives stacked on top of each other like a cake with layers that can share their data together.
  11. 11. Features Of RAID Levels: RAID 0 – Data Striping RAID 1 - Mirroring RAID 2 – Hamming Code RAID 3 – Single Check Disk per Group There are more lavels like 4,5,6 10.
  12. 12. RAID Level 0:
  13. 13. RAID level 0: Simplest RAID implementation Includes striping but no redundancy Highest-performance High risk of data loss Multiple drives involved Could lose all data in array with one drive failure
  14. 14. Cont………..!! Block level striping Notes: If two different I/O requests are pending for two different blocks of data, in all likelihood the two blocks are located in two different disks, then the requests can be issued in parallel If a single request is spread across multiple logically contiguous strips, the request can be handled in parallel.
  15. 15. Recommended Applications Video Production and Editing Image Editing Pre-Press Applications gaming systems. Disadvantage: Relaibility problem –no mirroring or parity bits. Advantage: speed enhancement Maximum utilization of physical drive storage capacity, because no room is taken for redundant data or data-parity storage
  16. 16. RAID Level1:
  17. 17. RAID Level 1: Highest level of redundancy Each drive has a mirrored copy in array No striping at this level Improves read performance over single disks because multiple disks can be read at once Slower write performance because two disks must be accessed for each modified data item to maintain mirroring High storage overhead Only half array stores unique data Most suitable where reliability is primary concern.
  18. 18. Cont……..!!!!!! Performance: If we use independent disk controllers for each disk, then we can increase the read or write speeds by doing operations in parallel.
  19. 19. Application: Accounting Financial Advantage: Provide best Performance Provide Fault tolerance Disadvantage: High cost. Requires twice the disk space
  20. 20. RAID Level 2:
  21. 21. RAID Level 2: Implements redundancy via striping Striped at bit level Uses Hamming ECC to check data integrity ECC data stored on separate drive Significant overhead in storage and performance . RAID 2 is the only RAID level that can repair errors, the other RAID levels can only detect them
  22. 22. Cont……….!!!!! Read – all disks are simultaneously accessed Write - all disks are simultaneously accessed Write penalty – computation of the Hamming ECC Used when many disk errors occur, but given the high reliability of individual disks, rarely used.
  23. 23. Advantages: Random Read Performance= Fair Sequential Read Performance= Very Good Sequential Write Performance= Very Good Disadvantages : Random Write Performance= Poor Requires a complex controller High overhead for check disks Not used in modern systems
  24. 24. RAID Level 3:
  25. 25. RAID Level 3: Also stripes at the byte level Uses XOR to calculate parity for ECC Much simpler than Hamming ECC Requires only one disk for parity information regardless of the size of the array Cannot determine which bit contains error, but this information can be gathered easily by inspecting the array for a failed disk High transfer rates, but only one request serviced at a time
  26. 26. Cont………!!! In the case of a disk failure, All data are available  missing data can be calculated from the parity bit Write: just maintain the parity such that later it can be regenerated. Failed disk to be replaced and the data regenerated
  27. 27. Cont….!!!!!!!!!! BYTE level striping and XOR ECC allows for one check disk: lowest overhead possible Example… A:0101 XOR B:0011 = Check:0110 A is gone? B:0011 XOR Check:0110 = 0101 (A)

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