LaCie 131018 - StorView Snapshot - Mac, User Manual

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Statistics
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15.3 Command Size - Alignment Statistics
Command size statistics express the percentage of commands whose size is as specified. The Alignment
statistics is the percentage of commands whose address aligned on the specified address boundary.
Figure 15–2 Statistics Screen - Command Size/Alignments Tab
Statistic Description
Command Size Expressed in the percentage of commands whose size is
specified for reads and writes. The values are displayed with
a horizontal bar for each value. The lack of a bar displayed for
a specific value indicates it is 0% (or less than 1%).
For example, consider a read or write command from a host
system with Logical Block Address (LBA) 0x0000070, and
access size 0x80, expressed in decimal 128. Using 512 byte
blocks on the disk drives, it can be seen that this is a read of
64 Kbytes, which is the command size.
Alignment This is the percentage of commands whose address is aligned
on the specified chunk boundary. The alignment of a
command from a host system is determined by the
command’s address.
In an optimal system, a write of one chunk of data would
reside exactly within a chunk on one disk. However, if this is
not the case, this write will be split up into two separate writes
to two different data drives. This of course will have a negative
effect on performance. To overcome these problems, the user
can, with more sophisticated operating systems, set the
access size and alignment to an optimal value. These
statistics can help the user to tune the operating system.