On 7/22/05 12:47 PM, "Mark Wong" <[EMAIL PROTECTED]> wrote:

> On a single spindle:
> $ time dd if=/dev/zero of=bigfile bs=8k count=2000000
> 2000000+0 records in
> 2000000+0 records out
> real    2m8.569s
> user    0m0.725s
> sys     0m19.633s

This is super fast!  124MB/s seems too fast for true write performance on a
single spindle.
> But here are some number for my 12-disk lvm2 striped volume.

So, software striping on how many controllers?
> $ time dd if=/dev/zero of=bigfile3 bs=8k count=4000000
> 4000000+0 records in
> 4000000+0 records out
> real    1m17.059s
> user    0m1.479s
> sys     0m41.293s

Again - super fast at 416MB/s.  How many controllers?

When we had our problems with the cciss driver and the smartarray 5i/6
controllers, we found the only way to get any performance out of them was to
run them in JBOD mode and software stripe.  However, when we did so the CPU
usage skyrocketed and the performance of simple SCSI adapters was 50% faster
with less CPU consumption.  These numbers show 100*(42.8/67) = 64% CPU
consumption, I'd expect less with 2 simple U320 SCSI controllers.

- Luke

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