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Date:      Thu, 8 Mar 2012 17:50:51 +0000
From:      Tom Evans <tevans.uk@googlemail.com>
To:        Dan Rue <drue@therub.org>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: ZFS and mdconfig -t vnode - Unexpected behavior
Message-ID:  <CAFHbX1KkonKGyjgYBMxj=-Kn9GNdKr%2BT5GYDMvhNo-Deq6BUsA@mail.gmail.com>
In-Reply-To: <20120308161940.GA71851@therub.org>

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On Thu, Mar 8, 2012 at 4:19 PM, Dan Rue <drue@therub.org> wrote:
> I have discovered an unexpected behavior when using ZFS against a vnode.
> When running mdconfig -d against a vnode, there is a long delay before
> the blocks are fully written to the backing store file. Consider the
> following test script:
>
> […]
>
> Are there any ZFS tunables that could be related to this? What could be
> the cause of this behavior?
>

The tunable vfs.zfs.txg.timeout (in seconds) controls how bursty ZFS
is. I run with a high value (30), so my disks don't get constantly
hit, but if you lowered it, data will be written much more frequently.

Cheers

Tom


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