Disk IO issues

[Matt Domsch]

On Sun, Jan 04, 2009 at 03:02:55AM +0000, Kostas Georgiou wrote:
> On Sat, Jan 03, 2009 at 06:32:38PM -0600, Matt Domsch wrote:
> 
> > What ext3 journaling options are enabled (e.g. what does 'mount' say)?
> > If it's data=ordered (the default), that's OK.  If it's data=journal,
> > then all the data gets written twice (first to the journal, then the
> > journal to the disk), which is really really slow, and the size of the
> > journal would really make a difference too.
> 
> For an NFS server (assuming that you aren't exporting as async)
> data=journal can give you better performance than anything else
> actually. The NFS howto has a brief note in the performance section
> about this.

Yes, if the slowness is seen by applications on the client side of the
NFS server, data=journal on the NFS server can help.

Mike, your tests were all on the local file system, not across an NFS
connection, right?

data=journal can only buffer up to the size of the journal.  Given the
comments about speed with "large files", unless the journal is
specifically tuned to be large enough to handle them, no dice.


-- 
Matt Domsch
Linux Technology Strategist, Dell Office of the CTO
linux.dell.com & www.dell.com/linux