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From: Jonathan Belson <jon@witchspace.com>
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Date: Sun, 14 Feb 2010 20:33:37 +0000
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To: Artem Belevich <fbsdlist@src.cx>
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Cc: freebsd-stable@freebsd.org
Subject: Re: More zfs benchmarks
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On 14 Feb 2010, at 20:26, Jonathan Belson wrote:

> On 14 Feb 2010, at 19:13, Artem Belevich wrote:
>> Can you check if kstat.zfs.misc.arcstats.memory_throttle_count sysctl
>> increments during your tests?
>>=20
>> ZFS self-throttles writes if it thinks system is running low on
>> memory. Unfortunately on FreeBSD the 'free' list is a *very*
>> conservative indication of available memory so ZFS often starts
>> throttling before it's really needed. With only 2GB in the system,
>> that's probably what slows you down.
>=20
> I tested a number of times during a 2GB write to a zfs partition and =
the count stayed at 0.

Oh, I should add that I use the following settings from the zfs tuning =
guide:

vm.kmem_size=3D"1024M"
vm.kmem_size_max=3D"1024M"
vfs.zfs.arc_max=3D"100M"

Cheers,

--Jon