O_SYNC behavior?

[Christoph Hellwig]

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.