Date: Fri, 6 Nov 2009 15:31:08 -0500 From: Ben Kelly <ben@wanderview.com> To: Michael Loftis <mloftis@wgops.com> Cc: freebsd-stable@freebsd.org Subject: Re: Performance issues with 8.0 ZFS and sendfile/lighttpd Message-ID: <696A0DF1-020B-48CB-BF38-6605EAD5BF1E@wanderview.com> In-Reply-To: <5275583A0E66749DA096A22F@[192.168.1.44]> References: <772532900-1257123963-cardhu_decombobulator_blackberry.rim.net-1402739480-@bda715.bisx.prod.on.blackberry> <hcma4s$c49$1@ger.gmane.org> <4AEEBD4B.1050407@quip.cz> <hcmhbj$40s$1@ger.gmane.org> <5275583A0E66749DA096A22F@[192.168.1.44]>
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On Nov 6, 2009, at 2:53 PM, Michael Loftis wrote: > --On Monday, November 02, 2009 12:55 PM +0100 Ivan Voras <ivoras@freebsd.org > > wrote: > >> Do you have actual disk IO or is the vast majority of your data >> served >> from the caches? (actually - the same question to the OP) > > That's the problem 64GB of RAM and ZFS doesn't seem to use any > cache. It also seems to not be realizing when multiple reads are on > the same block (same issue sorta) and dispatches the same I/O request. Have you tried adjusting vfs.zfs.arc_meta_limit? I've noticed the default value for this is set poorly when the overall ARC size is small. This happens because various structure's not actually allocated from the ARC like dnodes and dbufs are included in the metadata usage stats. When the ARC is large this is somewhat negligible, but for small ARCs it overwhelms the calculated default metadata limit and you end up not caching any real file system metadata. You could try increasing the metadata limit or even better increase your maximum ARC size to something over 1GB. (I seem to remember your ARC size is 128M from earlier in the thread). Hope that helps. - Ben
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