[CentOS] OT: Caching synchronous writes

Les Mikesell lesmikesell at gmail.com
Sat Apr 24 20:53:11 UTC 2010


Ross Walker wrote:
> On Apr 24, 2010, at 4:34 PM, Les Mikesell <lesmikesell at gmail.com> wrote:
> 
>> Ross Walker wrote:
>>> On Apr 24, 2010, at 12:43 PM, Les Mikesell <lesmikesell at gmail.com>
>>> wrote:
>>>
>>>> Ross Walker wrote:
>>>>> NFS should always be 'sync' if performance isn't good, then your
>>>>> storage isn't good.
>>>> Why demand sync on remote storage when you typically don't have it
>>>> locally?
>>>> Programs that need transactional integrity should know when to fsync
>>>> () and for
>>>> anything else there's not much difference whether you crash before
>>>> or after a
>>>> write() was issued in terms of it not completing.
>>> Yes, but 'async' ignores those fsyncs and returns immediately.
>> That sounds like a bug in the nfs client code if fsync() doesn't  
>> block until all
>> of the data is committed to disk.
> 
> It's not the client side I'm talking about, but the server side. We  
> were talking NFS servers and exporting sync (obey fsyncs) vs async  
> (ignore fsyncs).
> 
> The client always mounts async, that's not the problem.

That's different.  I thought the nfs spec was always sync on the server side and 
the client says when async is OK.  And there's some special case response to 
handle the case where the server rebooted between the async writes and the 
subsequent fsync().

-- 
   Les Mikesell
    lesmikesell at gmail.com



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