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Re: O_SYNC behavior?

To: Matthias Schniedermeyer <ms@xxxxxxx>
Subject: Re: O_SYNC behavior?
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 27 Apr 2010 10:12:05 -0400
Cc: Nathan Scott <nathans@xxxxxxxxxx>, xfs@xxxxxxxxxxx, Ray Van Dolson <rvandolson@xxxxxxxx>
In-reply-to: <20100427093250.GA15182@xxxxxxx>
References: <20100426225627.GA7106@xxxxxxxx> <537687191.239471272324343715.JavaMail.root@xxxxxxxxxxxxxxxxxx> <20100427093250.GA15182@xxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
On Tue, Apr 27, 2010 at 11:32:50AM +0200, Matthias Schniedermeyer wrote:
> 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".

The client side (that is mount-side) sync means implying O_SYNC for all
I/O - no need for that.  And sync exports are the default for every sane
server.

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