Today we continue our discussion on storage engineering
291) A RAID level 0 uses data striping to increase maximum bandwidth available. No redundant information is maintained
292) A RAID level 1 uses two copies of the data. This type of redundancy is often called mirroring There can be combinations of level 0 and 1 where like in level 1, read requests can be scheduled to both the disk and its mirror image and bandwidth for contiguous blocks is improved from the aggregation of all the disks.
293) A RAID level 2 uses a striping unit as a single bit. The number of check disks grows logarithmically with the number of data disks.
294) A RAID level 3 uses a bit inter-leaved parity where it keeps more redundant information than is necessary. Instead of using several disks to store hamming code that informs which disk has failed, we rely on that information from the disk controller and use a single check disk with parity information which is the lowest overhead possible.
295) A RAID level 4 uses a block inter-leaved parity with a striping unit of a disk block. Block-level striping has the advantage that read requests the size of a disk block can be served entirely by the disk where the requested block resides. The write of a single block still requires a read-modify-write cycle, but only one data disk and the check disk are involved and the difference between the old data block and the new data block is noted
296) A RAID level 5 uses a block inter-leaved distributed parity. The parity blocks are distributed uniformly over all disks, instead of sorting them on a single check disk. This has two advantages. First, several write requests potentially be processed in parallel, since the bottleneck of a unique check is removed. Second, read requests have a higher degree of parallelism. This level usually has the best performance.
291) A RAID level 0 uses data striping to increase maximum bandwidth available. No redundant information is maintained
292) A RAID level 1 uses two copies of the data. This type of redundancy is often called mirroring There can be combinations of level 0 and 1 where like in level 1, read requests can be scheduled to both the disk and its mirror image and bandwidth for contiguous blocks is improved from the aggregation of all the disks.
293) A RAID level 2 uses a striping unit as a single bit. The number of check disks grows logarithmically with the number of data disks.
294) A RAID level 3 uses a bit inter-leaved parity where it keeps more redundant information than is necessary. Instead of using several disks to store hamming code that informs which disk has failed, we rely on that information from the disk controller and use a single check disk with parity information which is the lowest overhead possible.
295) A RAID level 4 uses a block inter-leaved parity with a striping unit of a disk block. Block-level striping has the advantage that read requests the size of a disk block can be served entirely by the disk where the requested block resides. The write of a single block still requires a read-modify-write cycle, but only one data disk and the check disk are involved and the difference between the old data block and the new data block is noted
296) A RAID level 5 uses a block inter-leaved distributed parity. The parity blocks are distributed uniformly over all disks, instead of sorting them on a single check disk. This has two advantages. First, several write requests potentially be processed in parallel, since the bottleneck of a unique check is removed. Second, read requests have a higher degree of parallelism. This level usually has the best performance.
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