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Date:      Sat, 9 Jan 2010 19:40:53 -0500
From:      Garrett Moore <garrettmoore@gmail.com>
To:        freebsd-stable <freebsd-stable@freebsd.org>
Subject:   Re: ZFS performance degradation over time
Message-ID:  <7346c5c61001091640w1a0ffb5y3ffe97cb88c76436@mail.gmail.com>
In-Reply-To: <2ae8edf31001091051l156cb57alf549cfe06f1c7197@mail.gmail.com>
References:  <7346c5c61001030842r7dc76199y51e4c1c90a3eea6e@mail.gmail.com> <hi2nsf$do5$1@ger.gmane.org> <7346c5c61001080831w375d158fu5b1996ee58cb0f8d@mail.gmail.com> <ed91d4a81001080940ybfe1a63nc13bee5bd3136984@mail.gmail.com> <2ae8edf31001091051l156cb57alf549cfe06f1c7197@mail.gmail.com>

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After being up for a few days and having good performance, I turned on
rTorrent and downloaded two 700MB files. After these torrents completed, my
performance has tanked again. My combined read/write speed to the array
won't exceed about 25MB/s.

It seems that after having downloaded a few torrents, resources are grabbed
and then not released. From top:
Mem: 2326M Active, 962M Inact, 484M Wired, 82M Cache, 418M Buf, 87M Free

Nothing in userland is using a significant amount of memory. eg rTorrent is
using 41MB according to top. Killing rTorrent does not alleviate the
performance problems.

arcstats.size is hovering around 30-40MB.

[root@leviathan ~]# sysctl kstat.zfs.misc.arcstats.size
kstat.zfs.misc.arcstats.size: 28953448
[root@leviathan ~]# sysctl vm.stats.vm.v_inactive_count
vm.stats.vm.v_inactive_count: 237831
[root@leviathan ~]# sysctl vm.stats.vm.v_active_count
vm.stats.vm.v_active_count: 595762
[root@leviathan ~]# sysctl vm.stats.vm.v_cache_count
vm.stats.vm.v_cache_count: 21472


If no-one has any questions, I'll try Artem's suggestion of wasting a bunch
of memory in Perl/Python and forcing some memory to be swapped out. (I don't
want to do it yet in case someone wants a specific number before I do that).



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