Low nfs write throughput

[Bengt Ahlgren]

Daryl Sayers <daryl at ci.com.au> writes:

> Can anyone suggest why I am getting poor write performance from my nfs setup.
> I have 2 x FreeBSD 8.2-STABLE i386 machines with ASUS P5B-plus mother boards,
> 4G mem and Dual core 3g processor using 147G 15k Seagate SAS drives with
> onboard Gb network cards connected to an idle network. The results below show
> that I get nearly 100Mb/s with a dd over rsh but only 15Mbs using nfs. It
> improves if I use async but a smbfs mount still beats it. I am using the same
> file, source and destinations for all tests. I have tried alternate Network
> cards with no resulting benefit.

[...]

> Looking at a systat -v on the destination I see that the nfs test does not
> exceed 16KB/t with 100% busy where the other tests reach up to 128KB/t.
> For the record I get reads of 22Mb/s without and 77Mb/s with async turned on
> for the nfs mount.

On an UFS filesystem you get NFS writes with the same size as the
filesystem blocksize.  So an easy way to improve performance is to
create a filesystem with larger blocks.  I accidentally found this out
when I had two NFS exported filesystems from the same box with 16K and
64K blocksizes respectively.

(Larger blocksize also tremendously improves the performance of UFS
snapshots!)

Bengt