>>> Can you post the "time dd if=/dev/zero of=bigfile bs=8k count=500000"
>>> results? Also do the reverse (read the file) with "time dd if=bigfile
>>> of=/dev/null bs=8k".
>
> I didn't see this come across before... here ya go:
>
> time dd if=/dev/zero of=bigfile bs=8k count=500000
>
> 500000+0 records in
> 500000+0 records out
>
> real 1m52.738s
> user 0m0.310s
> sys 0m36.590s
So, that's 35MB/s, or 1/2 of a single disk drive.
> time dd if=bigfile of=/dev/null bs=8k
>
> time dd if=bigfile of=/dev/null bs=8k
> 500000+0 records in
> 500000+0 records out
>
> real 4m38.742s
> user 0m0.320s
> sys 0m27.870s
And that's 14MB/s, or < 1/4 of a single disk drive.
> FYI on your hardware raid comment... I easily get 50 megs a second on my
> 3ware controllers and faster on my LSI SATA controllers.
Then you are almost getting one disk worth of bandwidth.
By comparison, we get this using Linux software RAID on Xeon or Opteron:
$ time dd if=/dev/zero of=bigfile bs=8k count=500000
500000+0 records in
500000+0 records out
real 0m26.927s
user 0m0.074s
sys 0m8.769s
$ time dd if=bigfile of=/dev/null bs=8k
500000+0 records in
500000+0 records out
real 0m28.190s
user 0m0.039s
sys 0m8.349s
with less CPU usage than HW SCSI RAID controllers.
- Luke
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