the performance of SAS is not better than SCSI in FreeBSD, WHY?

Tzu-Hua Wang biogary at
Wed Apr 11 09:45:05 UTC 2007

Thank you for your response.
Ther performance of your server is significantly better than mine.
The SAS Chip of my HP ProLiant DL380 G5 is Smart HP Smart Array P400.
It uses the FreeBSD driver ciss0

I think that there is only one difference between your HP server and mine.
I configure my SAS HD as RAID 0.
Will this affect the performance?

Thank you

2007/4/11, Ivan Voras <ivoras at>:
> Tzu-Hua Wang wrote:
> > Generally, the performace of SAS in FreeBSD is far worse than SCSI in
> > FreeBSD.
> > Is it normal? How can I do to improve the performance of SAS HD in
> FreeBSD?
> There's a huge number of possible reasons - unless you're testing the
> same controller (I think there exist SAS+SCSI controllers, I might be
> wrong), you can't conclude that the SAS interface is less supported.
> For what it's worth, I've got approximately the same numbers on DL380
> G5, but I've attributed them to 2.5" small form factor drives.
> 2x 2.5" 10k RPM, CISS hw RAID1          2x 3.5", 7.5k RPM, soft RAID1
> Full stroke             3.863 ms        5.942 ms
> Half stroke             3.929 ms        6.186 ms
> Quarter stroke          3.998 ms        5.700 ms
> Short forward           3.889 ms        4.060 ms
> Short backward          4.715 ms        4.748 ms
> Seqential outer         1.011 ms        0.167 ms
> Sequential inner        1.013 ms        0.177 ms
> Read transfer, outside  43.6 MB/s       61.2 MB/s
> Read transfer, middle   38.8 MB/s       54.8 MB/s
> Read transfer, inside   32.8 MB/s       34.9 MB/s
> The 3.5" drives were SATA in a different machine (Dell's). It might be
> that the CISS driver is unreasonably slow, which is kind of possible
> given the suspicious lower bound of about 1 ms in seeks. Maybe something
> is throttling the I/O rate?

More information about the freebsd-hardware mailing list