Re: Fedora 8.0.1 XFS Tune on HW RAID for Max Write Throughput?

[David Chinner <dgc@sgi.com>]

On Sat, Dec 15, 2007 at 10:35:20PM -0600, Eric Sandeen wrote:
> Alex Madarasz wrote:
> > We're building a new Fedora 8.0.1 Linux system to stream data from a
> > 250Msps ADC to disk, and want to start tuning the system configuration
> > for maximum XFS write performance.  To date, without any significant
> > effort at tuning our Fedora 7 dev system, we're seeing 250MBps write
> > with 8-bit samples and ~ 300MBps write with 16-bit samples. We want to
> > push the tuning as far as we can go with this architecture before we
> > start looking at other hardware options.  Looking at various other
> > tuning pages on the Web finds few that are interested in maxing out
> > sequential writes to very large arrays while using SAS HW RAID with big
> > fast SAS drives too.
> 
> ...
> 
> > XFS Tuning Options?
> > 
> > - HW RAID0:
> >   - Array/logical disk HW RAID stripe size?
> 
> At any rate you'll want to match xfs's geometry with the raid geometry.
> 
> >   - Cache enabled (some reports that cache s/b turned off?)?
> 
> If it's battery-backed cache, leave it on, and disable barriers in xfs
> (it's a mount option)
> 
> >   - xfs mkfs / mount options?
> 
> David mentioned these before as a generic place to start:
> 
> # mkfs.xfs -f -l lazy-count=1,version=2,size=128m -i attr=2 -d agcount=4
> <dev>
> # mount -o logbsize=256k <dev> <mtpt>
> 
> and that those would be upcoming new defaults for mkfs.
> 
> 4 ags may not be what you want for a ~2T filesystem.

Right - the 4 AG tuning is effectively for single disk configurations to
limit parallelism and therefore keep seeks between AGs down. When you
have multiple disks, the [new] mkfs defaults should be just fine (i.e.
just drop the agcount suggestion).

Cheers,

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