[Linux-cluster] More GFS2 tuning...
jeff.sturm at eprize.com
Mon Feb 16 19:26:32 UTC 2009
> -----Original Message-----
> From: linux-cluster-bounces at redhat.com
> [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Corey Kovacs
> Sent: Monday, February 16, 2009 1:55 PM
> To: linux-cluster at redhat.com
> Subject: [Linux-cluster] More GFS2 tuning...
> By my reckoning, I should be able to see 400MB or more
> sustained throughput using this setup. If this is a pipe
> dream, someone let me know quick before I go nutz.
What do you get from the raw device? (I.e. if you remove GFS/NFS from
> The bo values start at around 200MB, then drop down to 0 in
> most cases for a few seconds, then spike to ~700MB/s then
> eases back down to 200, 150 and back down to 0. It looks very
> much like a cacheing issue to me.
Linux virtual memory does some funny things with fs caching. Try some
tests with O_DIRECT to bypass the buffer cache. On RHEL 5 systems, you
can achieve that with "dd ... oflag=direct" and varying block sizes.
> I've read that GFS2 is supposed to be "self tuning" but I
> don't think these are necessarily GFS2 issues.
Agreed. If you can experiment with the hardware, what do you get from
other fs types? (such as ext3)
> Anyone have something similar? What I/O rates are people getting?
I don't have any FC hardware quite as nice as yours, but multipathing
AoE over a pair of GigE connections we can get 200MB/s raw, sequential
throughput. (I.e. about the limits of the interconnects.)
My GFS filesystems are mostly a collection of very small (~1MB or less)
files, so, it's hard to say how they are performing. I'm much more
concerned about the rate of file creates over GFS than raw throughput
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