LaCie 131018 - StorView Snapshot - Mac, User Manual

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StorView RAID Module
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How to Use Command Size and
Alignment To calculate the alignment, we check the LBA for the largest
number of blocks that will evenly divide into it, in powers of 2.
So, we can see that in this case, the alignment is 0x10 = 16
blocks. This equates to 8K.
The alignment, in conjunction with the access size, gives an
indication of how many drives are involved in an access. In the
above example, consider a RAID 5/50/6 array with a chunk
size of 64K. In this case, the above access will actually involve
2 data drives, since it needs to access 8K in the first drive
(0x80 – 0x70 = 0x10 blocks = 8K), and the remaining 56K in
the next drive (0x70 blocks = 56K). This is clearly inefficient,
and could be improved by setting the alignment to 64K on the
operating system. If that is not possible, using a larger chunk
size can help, as this reduces the number of accesses that
span chunks. Aligning an access on the same value as the
access size will improve performance, as it will ensure that
there are no multi-chunk accesses for commands that are
smaller than a chunk size.
Statistic Description