Re: [patch] Re: Does XFS prevent disk spindown?

[David Chinner <dgc@sgi.com>]

On Wed, Apr 09, 2008 at 11:32:34PM +0200, Thor Kristoffersen wrote:
> David Chinner <dgc@sgi.com> writes:
> >>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> >> realtime =none                   extsz=4096   blocks=0, rtextents=0
> >> 
> >> Is that what's causing it?  I have never specified any lazy-count option
> >> when I created or mounted the filesystem.  I didn't even know it existed.
> >
> > Introduced in 2.6.22, and recently was made the default mkfs config.
> >
> > Try the patch below.
> 
> Thanks a lot, David!  Your patch worked perfectly.  Also thanks to the
> others who helped me track down this issue.

Cool. I'll get that patch reviewed and checked in, then.

> BTW, what are the consequences of setting lazy-count to 0?  Less safety?
> Reduced performance?

One a single disk? No difference to performance, but significantly
lower latency on metadata operations is seen when using lazy-count=1.

If you have lots of disks, or low-latency caches in front of your disks,
lazy-count=1 will prevent superblock updates from being the metadata
performance limiting factor.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group