[magick-users] Transfer size considered harmful

[Gabe Schaffer]

On 2/27/07, Seth Price <seth at pricepages.org> wrote:

> The numbers I'm getting:
> 4.00 KB per transfer
> ~750 transfers per second (trashing)
> ~3 MB per second
> < 25% CPU utilization
>
> The disk that is being used is a fairly recent SATA II disk. You can
> immediately see from the numbers that something is very wrong with
> the max throughput. I am guessing that the problem is in the transfer
> size. Documentation that I read said that the rule of thumb is to
> keep it below 200 transfers per second, and the block size is
> normally closer to 128 KB.

While possible, I find it unlikely that the transfer size is the
problem here. More than likely it is disk seek bandwidth. Your SATA II
drive may be able to transfer 60MB/s when reading sequentially, but if
the head has to seek you're probably moving it around too much. I
would expect 100% CPU utilization (unless you have a
quad-core/CPU/thread machine) if the transfer size were the problem.
The only way to fix this is to get more spindles (i.e. RAID with
striping) or more RAM.

GNS