[arch-general] NFS close-to-open

Bryan Schumaker bjschuma at gmail.com
Mon Dec 10 09:26:51 EST 2012

On 12/10/2012 08:11 AM, Paul Gideon Dann wrote:
> I've been learning about the close-to-open policy of NFS, which causes each 
> file to be flushed to the server as it's closed, to ensure consistency across 
> clients.  This is a big performance hit when trying to upgrade the system, 
> because of the numerous writes to small files.
> I know about the "async" export option, obviously, but there is also a "nocto" 
> client mount option, which is supposed to disable the close-to-open mechanism 
> for that client.  As far as I can tell, this is supposed to stop the client 
> from flushing the file when it closes it (as well as not bothering to check 
> cache consistency when it opens).  However, this seems to have no effect: the 
> client is still flushing the file to the server on close, causing massive 
> wait-io.
> Does anyone have any idea why "nocto" doesn't have the effect I was hoping it 
> would?  The "async" option works as expected, but it's more important to me 
> that the client cache is correct, and it just bugs me.
What NFS version are you using?  I just took a quick glance through the code and from what I can tell, v2 and v3 check for the "nocto" flag but v4 doesn't.  I'm not sure if this is an oversight or by design, but I can ask later today.

- Bryan

> Thanks for any insight,
> Paul

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