Re: NFS write throughput not constant

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Can be related to flushing of dirty pages. 
How much memory do you have on the clients?

You can play with vm.dirty_background_bytes
kernel parameter to get better performance.
Linux default is 10% of the RAM
(vm.dirty_background_ratio ), which can produce
spikes on IO if too much data accumulated in
fs cache, while you, probably, smooth continues
writing.

Tigran.


----- Original Message -----
> From: "Fu, Yong" <yong.fu@xxxxxxxxx>
> To: linux-nfs@xxxxxxxxxxxxxxx
> Sent: Friday, September 9, 2016 7:34:54 AM
> Subject: NFS write throughput not constant

> Hi,
> I have some test on 10Gbe against NFS-based storage recently, and found the
> throughput of writing was not constant, the performance of writing drop down
> periodically.
> My nfs client(version 3 and version 4 all tried) resident CentOS
> 6.6(2.6.32-504.el6.x86_64), NFS server is OpenMediaVault(5 ssd with stripe)
> 
> On a single mount point(or single nfs client), the avg throughput only can reach
> 430 MB/s, and two nfs clients aggregation can reach 700 MB/s, I can see there
> is periodical drop of network traffic graph both client and server side, and I
> am sure it's a nfs issue by lots of other tests.
> 
> I also found the nfs client commit procedure happened at the time that writing
> performance also dropped, and I have read B7
> section(http://nfs.sourceforge.net) and think the relationship between them,
> but no many ideas,  can someone help me pinpoint the root cause of this issue?
> 
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