PE2950, LSI SAS -> SATA very slow

Bond Masuda bond.masuda at jlbond.com
Fri Apr 30 11:34:11 CDT 2010


> We have a PowerEdge 2950 with an "LSISAS1068E" controller, hooked up to
> two Seagate 1TB SATA disks.  For some reason the performance of these
> disks is quite poor - I'm lucky to get over 10MB/sec from them, when I
> should be getting closer to 100MB/sec.

10MB/sec does seem extremely poor. we've had read slowness when Linux block
device read-ahead was too small. Once properly configured, performance on
RAID-5 went from 150MB/sec to 500MB/sec, so the difference is dramatic. we
usually tune read-ahead (in Linux) buffers starting from 8MB to 32MB and
benchmark to see what works best. but your problem may be elsewhere... we've
never seen 10MB/sec...

> Having recently had a bad experience with one of Dell's SATA RAID
> controllers (of which I wasn't the only one), I'm wondering whether
> this
> is going to be a repeat of that?  Does anyone have a SAS controller
> similar to this with SATA disks?  Does it also suffer poor throughput
> or
> is it just me?

On the PERC5/I, 8x HDD, RAID-5, we can get 400-500MB/sec sequential
read/writes. I believe PERC5/I uses the LSISAS1068E with a Intel IOP333.

-Bond



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