Re: NFS performance degradation of local loopback FS.

[Peter Staubach <staubach@redhat.com>]

Krishna Kumar2 wrote:
>>       200 processes:
>>     
>
> By "200 processes", I meant 200 dd's, each reading from /dev/zero and
> writing to a file on the filesystem. The script "nfs" was run twice, first
> with
> a local filesystem and the second time with the same filesystem NFS
> mounted.
>
>   

Well, you aren't exactly comparing apples to apples.  The NFS
client does close-to-open semantics, meaning that it writes
all modified data to the server on close.  The dd commands run
on the local file system do not.  You might trying using
something which does an fsync before closing so that you are
making a closer comparison.

All that said, yes, one would expect a slow down.  How much is
debatable and varies from platform to platform and load to load.

I would also advise care when running NFS like that.  It is
subject to deadlock and is not recommended.

       ps

> Thanks,
>
> - KK
>
> linux-nfs-owner@vger.kernel.org wrote on 06/19/2008 12:16:23 PM:
>
>   
>> Hi,
>>
>> I am running 2.6.25 kernel on a [4 way, 3.2 x86_64, 4GB] system. The test
>> is doing I/O on a local ext3 filesystem, and measuring the bandwidth, and
>> then NFS mounting the filesystem loopback on the same system. I have
>> configured 64 nfsd's to run. The test script is attached at the bottom.
>>
>> My configuration is:
>>       /dev/some-local-disk  :            /local
>>       NFS mount /local       :            /nfs
>>
>> The result is:
>>       200 processes:
>>             /local: 108000 KB/s
>>             /nfs:     66000 KB/s: Drop of 40%
>>
>>       300 processes (KB/s):
>>             /local: 112000 KB/s
>>             /nfs:    57000 KB/s: Drop of 50%
>>
>> I am not using any tuning, though I have tested with both
>> sunrpc.tcp_slot_table_entries=16 & 128
>>
>> Is this big a drop expected for a loopback NFS mount? Any
>> feedback/suggestions are very
>> appreciated.
>>
>> Thanks,
>>
>> - KK
>>
>> (See attached file: nfs)[attachment "nfs" deleted by Krishna
>>     
> Kumar2/India/IBM]
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>