[OpenAFS-devel] Patch to disable fsync()ing

[Dale Ghent]

On Mar 16, 2007, at 1:22 PM, Jim Rees wrote:

> The only reason to fsync would be to enforce a particular ordering  
> on the
> data written to disk.

For POSIX write semantics, yes?

>   But there is no question afs is way too aggressive at
> syncing.

The main reason behind Rob's fsync patch is because we're using ZFS  
on our AFS servers, all 8 of them.

ZFS's current behavior (in the future this will be dynamically  
alterable) when dealing with a fsync is that it will flush all  
pending IOs in the ZFS intent log (aka ZIL, a write cache) to disk,  
and this holds up subsequent write IOs until this is completed.  
Because we still run our per-user mail store out of ZFS, fsyncs are  
quite expensive because of the sheer amount of data (incoming mail)  
being written.

/dale

--
Dale Ghent
UNIX and Storage Systems Specialist
UMBC - Office of Information Technology
ENG 201 - 410-443-1705