Low nfs write throughput
Daryl Sayers
daryl at ci.com.au
Tue Nov 29 23:56:32 UTC 2011
>>>>> "John" == John Baldwin <jhb at freebsd.org> writes:
> On Monday, November 28, 2011 7:12:39 pm Daryl Sayers wrote:
>> >>>>> "Bengt" == Bengt Ahlgren <bengta at sics.se> writes:
>>
>> > 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!)
>>
>> Thanks to all that answered. I did try the 'sysctl -w vfs.nfsrv.async=1' with
>> no reportable change in performance. We are using a UFS2 filesystem so the
>> zfs command was not required. I did not try the patch as we would like to stay
>> as standard as possible but will upgrade if the patch is released in new
>> kernel.
> If you can test the patch then it is something I will likely put into the
> next release. I have already tested it as far as robustness locally, what
> I don't have are good performance tests. It would really be helpful if you
> were able to test it.
>> Thanks Bengt for the suggestion of block size. Increasing the block size to
>> 64k made a significant improvement to performance.
> In theory the patch might have given you similar gains. During my simple tests
> I was able to raise the average I/O size in iostat to 70 to 80k from 16k.
OK, I downloaded and install the patch and did some basic testing and I can
reveal that the patch does improve performance. I can also see that my KB/t
now exceed the 16KB/t that seemed to be a limiting factor prior.
--
Daryl Sayers Direct: +612 95525510
Corinthian Engineering Office: +612 95525500
Suite 54, Jones Bay Wharf Fax: +612 95525549
26-32 Pirrama Rd email: daryl at ci.com.au
Pyrmont NSW 2009 Australia www: http://www.ci.com.au
More information about the freebsd-stable
mailing list