Richard,
I disconnected all but one path and disabled mpxio via stmsboot -d and my read
performance doubled. I saw about 100MBps average from the pool.
BTW, single harddrive performance (single disk in a pool) is about 140MBps.
What do you think?
Thank you again for your help!
--- On Thu, 7/29/10, Richard Elling <rich...@nexenta.com> wrote:
From: Richard Elling <rich...@nexenta.com>
Subject: Re: [zfs-discuss] ZFS read performance terrible
To: "Carol" <holaaqu...@yahoo.com>
Cc: "zfs-discuss@opensolaris.org" <zfs-discuss@opensolaris.org>
Date: Thursday, July 29, 2010, 2:03 PM
On Jul 29, 2010, at 9:57 AM, Carol wrote:
> Yes I noticed that thread a while back and have been doing a great deal of
> testing with various scsi_vhci options.
> I am disappointed that the thread hasn't moved further since I also suspect
> that it is related to mpt-sas or multipath or expander related.
The thread is in the ZFS forum, but the problem is not a ZFS problem.
> I was able to get aggregate writes up to 500MB out to the disks but reads
> have not improved beyond an aggregate average of about 50-70MBps for the pool.
I find "zpool iostat" to be only marginally useful. You need to look at the
output of "iostat -zxCn" which will show the latency of the I/Os. Check to
see if the latency (asvc_t) is similar to the previous thread.
> I did not look much at read speeds during alot of my previous testing because
> I thought write speeds were my issue... And I've since realized that my
> userland write speed problem from zpool <-> zpool was actually read limited.
Writes are cached in RAM, so looking at iostat or zpool iostat doesn't offer
the observation point you'd expect.
> Since then I've tried mirrors, stripes, raidz, checked my drive caches,
> tested recordsizes, volblocksizes, clustersizes, combinations therein, tried
> vol-backed luns, file-backed luns, wcd=false - etc.
>
> Reads from disk are slow no matter what. Of course - once the arc cache is
> populated, the userland experience is blazing - because the disks are not
> being read.
Yep, classic case of slow disk I/O.
> Seeing write speeds so much faster that read strikes me as quite strange from
> a hardware perspective, though, since writes also invoke a read operation -
> do they not?
In many cases, writes do not invoke a read.
-- richard
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