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From: Peter Toth <freebsd@snap.net.nz>
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Subject: Re: NFS zfs serveur (hardware question)
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On 06/24/11 10:17, David Brodbeck wrote:
> On Wed, Jun 22, 2011 at 6:26 PM, Damien Fleuriot <ml@my.gd> wrote:
>> As a rule of thumb and for a serious server, I would recommend 1 SSD as dedicated cache and 2 SSD for a mirrored ZIL (you don't want to lose this data).
>> However I think ppl posted about running intro trouble when using both ZIL and cache disks, so I suggest you only get the ZIL.
> Definitely get the ZIL device.  NFS performance will be almost
> intolerable without it.  It used to be you could work around this, at
> cost of an increased risk of data loss if the server crashed, by
> turning off the ZIL; but as of 9.0 this is no longer allowed, so a ZIL
> device is pretty much mandatory.  I'm looking at ways to add one to
> one of my machines for this reason.
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There is still a way to increase NFS performance in 9.0 (without a ZIL
SSD) by setting zfs property "sync=disabled", which will disable
synchronous writes - comes with some risks, research it before switching
it off. Also, this will only disable sync for the ZFS filesystem not for
the whole pool.