Gateway 840 VT-100, Руководство пользователя

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Introduction
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is used, then the stripe size is 1MB (4 chunks × 256 K). So, for maximum
performance, the host could either send 5 × 1 MB write commands, or 20 ×
256 K write commands.
The effectiveness of the controller’s ability to perform a Full Stripe Write
depends on a number of parameters.
Sequential access
If the commands sent from the host are not sequential, the controller will not
be able to cluster them together. So, unless each individual access is sufficient
to fill a stripe, a Full Stripe Write will not occur.
Number of outstanding commands
For the controller to successfully cluster commands, there has to be a number
of write commands sent simultaneously. Setting the host to send up to 64
commands should prove adequate. Alternatively, enabling writeback cache will
have a similar effect, as the controller can then cluster sequential commands
even if the host only sends a small number of commands at a time.
Access size
With very small accesses, it is necessary to have a large number of commands
to cluster together to fill up a full stripe. So, the larger the access size the better.
It is best to use an access size that will fill a chunk. Of course, even if a stripe
is not filled up, small sequential writes will still benefit from command
clustering.
Access alignment
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
will have a negative effect on performance. To overcome these problems, you
can, with more sophisticated operating systems, set the access size and
alignment to an optimal value.