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Re: O_SYNC behavior?

To: Nathan Scott <nathans@xxxxxxxxxx>
Subject: Re: O_SYNC behavior?
From: Matthias Schniedermeyer <ms@xxxxxxx>
Date: Tue, 27 Apr 2010 11:32:50 +0200
Cc: Ray Van Dolson <rvandolson@xxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <537687191.239471272324343715.JavaMail.root@xxxxxxxxxxxxxxxxxx>
References: <20100426225627.GA7106@xxxxxxxx> <537687191.239471272324343715.JavaMail.root@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
On 27.04.2010 09:25, Nathan Scott wrote:
> 
> ----- "Ray Van Dolson" <rvandolson@xxxxxxxx> wrote:
> 
> > End-user question:
> > 
> > NFS client accessing an NFS export on an XFS based filesystem via
> > "sync" (O_SYNC) mode.
> > 
> > Will write confirmation be sent back from the NFS server when the
> > data is written to the xfs journal,
> 
> Data is never written to the journal.

I don't think that answers the intented question.

I guess the correct answer is:
It depends on the server-side configuration.
An "async" export gets the "done"-answer immediatly.
An "sync" export (only when also mounted "sync" AFAIU) waits at least 
until the write command is send down the stack, maybe even until the 
data actually hit the platters or silicon in the SSD-case.

man 5 exports:
- snip -
sync:   Reply to requests only after the changes have been committed to stable 
storage
- snip -

But i guess the performance will be horrible when both side are "sync".




Bis denn

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