Bit level striping split the bits of each byte across

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Bit-level striping  – split the bits of each byte across multiple disks In an array of eight disks, write bit  i  of each byte to disk  i. Each access can read data at eight times the rate of a single disk. But seek/access time worse than for a single disk Bit level striping is not used much any more Block-level striping   – with  n  disks, block  i  of a file goes to disk ( i   mod  n ) + 1 Requests for different blocks can run in parallel if the blocks  reside on different disks A request for a long sequence of blocks can utilize all disks in  parallel
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© Silberschatz, Korth and Sudarshan 10.25 Database System Concepts - 6 th  Edition RAID Levels Schemes to provide redundancy at lower cost by using disk  striping combined with parity bits Different RAID organizations, or RAID levels, have differing  cost, performance and reliability characteristics RAID Level 1 :   Mirrored disks  with block striping Offers best write performance.   Popular for applications such as storing log files in a database system. RAID Level 0 :   Block striping; non-redundant .    Used in high-performance applications where data loss is not critical
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© Silberschatz, Korth and Sudarshan 10.26 Database System Concepts - 6 th  Edition RAID Levels (Cont.) RAID Level 2 :   Memory-Style Error-Correcting-Codes  (ECC) with bit  striping. RAID Level 3 Bit-Interleaved Parity  a single parity bit is enough for error correction, not just  detection, since we know which disk has failed When writing data, corresponding parity bits must also be  computed and written to a parity bit disk To recover data in a damaged disk, compute XOR of bits  from other disks (including parity bit disk) 
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© Silberschatz, Korth and Sudarshan 10.27 Database System Concepts - 6 th  Edition RAID Levels (Cont.) RAID Level 3  (Cont.) Faster data transfer than with a single disk, but fewer I/Os per  second since every disk has to participate in every I/O.  Subsumes Level 2 (provides all its benefits, at lower cost).  RAID Level 4   Block-Interleaved Parity ; uses block-level striping,  and keeps a parity block on a separate disk for corresponding  blocks from  N  other disks. When writing data block, corresponding block of parity bits must  also be computed and written to parity disk To find value of a damaged block, compute XOR of bits from  corresponding blocks (including parity block) from other disks.
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© Silberschatz, Korth and Sudarshan 10.28 Database System Concepts - 6 th  Edition RAID Levels (Cont.) RAID Level 4  (Cont.)
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  • Fall '15
  • Sudarshan, Korth, Mac OS X, disk

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