On 2010-Jul-11 11:25:12 -0700, Richard Lee <ri...@csua.berkeley.edu> wrote: >But when almost all of the memory is taken by disk cache (of non-zfs >file system), ZFS disks start threshing like mad and the write >throughput goes down in 1-digit MB/second.
It can go a lot lower than that... Yes, this is a known problem. The underlying problem is a disconnect between the ZFS cache (ARC) and the VM cache used by everything else, preventing ZFS reclaiming RAM from the VM cache. For several months, I was running a regular cron job that was a slightly fancier version of the perl one-liner. I have been using the attached arc.patch1 based on a patch written by Artem Belevich <fbsdl...@src.cx> (see http://pastebin.com/ZCkzkWcs ) for about a month. I have had reasonable success with it (and junked my cronjob) but have managed to wedge my system a couple of times whilst doing zfs send|recv. Whilst looking at that diff, I just noticed a nasty signed/unsigned bug that could bite in low memory conditions and have revised it to arc.patch2 (untested as yet). Independently, Martin Matuska <m...@freebsd.org> committed r209227 that corrects a number of ARC bugs reported on OpenSolaris. Whilst this patch doesn't add checks on "inactive" or "cache", some quick checks suggest it also helps (though I need to do further checks). See http://people.freebsd.org/~mm/patches/zfs/head-12636.patch -- Peter Jeremy
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