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Date: Mon, 10 Jan 2011 13:33:51 +0000
From: Bruce Cran <bruce@cran.org.uk>
To: Ivan Voras <ivoras@freebsd.org>
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Cc: freebsd-performance@freebsd.org
Subject: Re: Phoronix comparision of HAMMER, UFS, ZFS, EXT3, EXT4, Btrfs
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On Mon, 10 Jan 2011 14:12:32 +0100
Ivan Voras <ivoras@freebsd.org> wrote:

> I've also noticed it is bursty - this can be moderated by tuning 
> vfs.zfs.txg.timeout and vfs.zfs.vdev.max_pending. But I think you
> must agree that 210 MB/s on a single drive looks impossible :) I get
> that much in a SAS RAID-10 configuration.

Exactly: since the disk obviously can't write at 210MB/s (115 seems to
be about its maximum) ZFS is buffering the data and then has to spend
time flushing it to disk during which time it can't accept any new IO
requests.

-- 
Bruce Cran