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Date:      Mon, 30 Apr 2012 07:09:43 +0200 (CEST)
From:      Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To:        Rick Macklem <rmacklem@uoguelph.ca>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: NFS - slow
Message-ID:  <alpine.BSF.2.00.1204300708060.30254@wojtek.tensor.gdynia.pl>
In-Reply-To: <1715805628.104139.1335733226336.JavaMail.root@erie.cs.uoguelph.ca>
References:  <1715805628.104139.1335733226336.JavaMail.root@erie.cs.uoguelph.ca>

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> the server is required to do that. (ie. Make sure the data is stored on
> stable storage, so it can't be lost if the server crashes/reboots.)
> Expensive NFS servers can use non-volatile RAM to speed this up, but a generic
> FreeBSD box can't do that.
>
> Some clients (I believe ESXi is one of these) requests FILE_SYNC all the
> time, but all clients will do so sooner or later.
>
> If you are exporting ZFS volumes and don't mind violating the NFS RFCs
> and risking data loss, there is a ZFS option that helps. I don't use
> ZFS, but I think the option is (sync=disabled) or something like that.
> (ZFS folks can help out, if you want that.) Even using vfs.nfsrv.async=1
> breaks the above.


thank you for answering. i don't use or plan to use ZFS. and i am aware of 
this NFS "feature" but i don't understand - even with syncs disabled, why 
writes are not clustered. i always see 32kB writes in systat


when running unfsd from ports it doesn't have that problem and works 
FASTER than kernel nfs.



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