stripe size & stripe width

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                下面这篇文章介绍的比较详细
http://www.pcguide.com/ref/hdd/perf/raid/concepts/perfStripe-c.html
Stripe Width and Stripe Size
RAID arrays that use
striping
improve performance by
splitting up files into small pieces and distributing them to multiple hard disks. Most
striping implementations allow the creator of the array control over two critical
parameters that define the way that the data is broken into chunks and sent to the various
disks. Each of these factors has an important impact on the performance of a striped
array.
The first key parameter is the stripe width of the array. Stripe width refers
to the number of parallel stripes that can be written to or read from simultaneously. This
is of course equal to the number of disks in the array. So a four-disk striped array would
have a stripe width of four. Read and write performance of a striped array increases as
stripe width increases, all else being equal. The reason is that adding more drives to the
array increases the parallelism of the array, allowing access to more drives
simultaneously. You will generally have superior transfer performance from an array of
eight 18 GB drives than from an array of four 36 GB of the same drive family, all else
being equal. Of course, the cost of eight 18 GB drives is higher than that of four 36 GB
drives, and there are other concerns such as power supply to be dealt with.
The second important parameter is the stripe size of the array, sometimes also
referred to by terms such as block size, chunk size, stripe length or
granularity. This term refers to the size of the stripes written to each disk.
RAID arrays that stripe in blocks typically allow the selection of block sizes in
kiB
ranging from 2 kiB to 512 kiB (or even
higher) in powers of two (meaning 2 kiB, 4 kiB, 8 kiB and so on.) Byte-level striping (as
in
RAID 3
) uses a stripe size of one byte or
perhaps a small number like 512, usually not selectable by the user.
               
               
               
               
               

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