NFS - slow

Wojciech Puchar wojtek at
Mon Apr 30 05:09:47 UTC 2012

> 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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