Re: SAN performance mystery

* John Vincent (pgsql-performance(at)lusis(dot)org) wrote:
> >> I'd have to agree with you about the specific SAN/setup you're working
> >> with there. I certainly disagree that it's a general property of SAN's
> >> though. We've got a DS4300 with FC controllers and drives, hosts are
> >> generally dual-controller load-balanced and it works quite decently.
> >>
> >How are you guys doing the load balancing? IIRC, the RDAC driver only does
> >failover. Or are you using the OS level multipathing instead? While we were
> >on the 4300 for our AIX boxes, we just created two big RAID5 LUNs and
> >assigned one to each controller. With 2 HBAs and LVM stripping that was
> >about the best we could get in terms of load balancing.

We're using the OS-level multipathing. I tend to prefer using things
like multipath over specific-driver options. I havn't spent a huge
amount of effort profiling the SAN, honestly, but it's definitely faster
than the direct-attached hardware-RAID5 SCSI system we used to use (from
nStor), though that could have been because they were smaller, slower,
regular SCSI disks (not FC).

A simple bonnie++ run on one of the systems on the SAN gave me this:
Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
vardamir 32200M 40205 15 22399 5 102572 10 288.4 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 2802 99 +++++ +++ +++++ +++ 2600 99 +++++ +++ 10205 100

So, 40MB/s out, 102MB/s in, or so. This was on an ext3 filesystem.
Underneath that array it's a 3-disk RAID5 of 300GB 10k RPM FC disks.
We also have a snapshot on that array, but it was disabled at the time.

> >Indeed, the EMC SANs are generally the high-priced ones too, so not
> >> really sure what to tell you about the poor performance you're seeing
> >> out of it. Your IT folks and/or your EMC rep. should be able to resolve
> >> that, really...
> >
> >
> >The only exception I've heard to this is the Clarion AX150. We looked at
> >one and we were warned off of it by some EMC gearheads.

Yeah, the Clarion is the EMC "cheap" line, and I think the AX150 was the
extra-cheap one which Dell rebranded and sold.

Thanks,

Stephen