[nfsv4] Performance drop in iozone for reading large files

[Dean Hildebrand]

So your server only has 1 GB of RAM in the original case?  If your
server only has 1 GB of RAM, then reading a file greater than 1 GB will
definitely reduce performance as the server is now going to disk.  Since
the server operating system also requires memory, it would be normal to
see a performance drop off much earlier, maybe around 600-800 MB.

Does this make sense, or do the original clients/servers have more than
1 GB of RAM?
Dean

Bryce Harrington wrote:
> The client and server for these tests are identical hardware, and we're
> booting them with the same kernel args, so we reduced the RAM the same
> on both client and server.
>
> We didn't try a 4GB file on the 4GB ram system yet.  I suppose we could
> also try reducing the memory on that system to <1GB and see what happens.
>
> Bryce
>
> On Fri, Aug 25, 2006 at 07:15:10PM -0400, Dean Hildebrand wrote:
>   
>> Just to clarify, are you referring to client memory below?  Does the 
>> amount of server memory affect the situation?  Did you try a 4GB file on 
>> the 4GB ram system?
>>
>> Dean
>>
>> Bryce Harrington wrote:
>>     
>>> There is a performance issue in READ operations we've noticed in iozone
>>> runs for a while now.  If you look at this plot, of NFSv4 with 1G mem:
>>>
>>>   http://crucible.osdl.org/runs/1604/test_output/iozone.sys.log.png
>>>
>>> You can see that we're getting fairly steady performance up until the
>>> 1048576kb case, where read performance drops to about a third.
>>>
>>> Is anyone else experiencing similar effects?
>>>
>>> Testing against NFSv3 shows similar behavior. 
>>>
>>> Also, from our tests it appears to be memory-related.  We booted with
>>> less memory and see the issue occuring for lower file sizes:
>>>
>>> NFSv3 w/ 256M mem:
>>>    http://crucible.osdl.org/runs/1607/test_output/iozone.nfsv3.log.png
>>>    -> Drops off at the 131072k file size
>>>
>>> NFSv3 w/ 512M mem:
>>>    http://crucible.osdl.org/runs/1612/test_output/iozone.nfsv3.log.png
>>>    -> Drops off at the 262144k file size
>>>
>>> On our 64-bit x86 systems with 4G RAM, we are not seeing the issue,
>>> presumably due to the larger memory size.
>>>
>>> NFSv4 w/ 4G mem:
>>>    http://crucible.osdl.org/runs/1511/test_output/iozone.sys.log.png
>>>    -> No drop off
>>>
>>> This issue has been present for a while now, but other issues had hidden
>>> it in recent iozone runs.
>>>
>>> Does anyone have an idea why the dropoff is occuring?  Is the memory
>>> size expected to affect NFS performance this way?  Is anyone else
>>> experiencing similar effects?
>>>
>>> Thanks,
>>> Bryce
>>> _______________________________________________
>>> NFSv4 mailing list
>>> NFSv4 at linux-nfs.org
>>> http://linux-nfs.org/cgi-bin/mailman/listinfo/nfsv4
>>>  
>>>       
>> -- 
>> Dean Hildebrand
>> Ph.D. Candidate
>> University of Michigan
>>     

-- 
Dean Hildebrand
Ph.D. Candidate
University of Michigan