Re: 3ware 9650 tips

[David Chinner <dgc@sgi.com>]

On Fri, Jul 13, 2007 at 03:36:46PM -0400, Justin Piszcz wrote:
> On Fri, 13 Jul 2007, Jon Collette wrote:
> 
> >Wouldn't Raid 6 be slower than Raid 5 because of the extra fault tolerance?
> >  http://www.enterprisenetworksandservers.com/monthly/art.php?1754 - 20% 
> >drop according to this article
> >
> >His 500GB WD drives are 7200RPM compared to the Raptors 10K.  So his 
> >numbers will be slower. 
> >Justin what file system do you have running on the Raptors?  I think thats 
> >an interesting point made by Joshua.
> 
> I use XFS:

When it comes to bandwidth, there is good reason for that.

> >>>Trying to stick with a supported config as much as possible, I need to 
> >>>run ext3.  As per usual, though, initial ext3 numbers are less than 
> >>>impressive. Using bonnie++ to get a baseline, I get (after doing 
> >>>'blockdev --setra 65536' on the device):
> >>>Write: 136MB/s
> >>>Read:  384MB/s
> >>>
> >>>Proving it's not the hardware, with XFS the numbers look like:
> >>>Write: 333MB/s
> >>>Read:  465MB/s
> >>>

Those are pretty typical numbers. In my experience, ext3 is limited to about
250MB/s buffered write speed. It's not disk limited, it's design limited. e.g.
on a disk subsystem where XFS was getting 4-5GB/s buffered write, ext3 was doing
250MB/s.

http://oss.sgi.com/projects/xfs/papers/ols2006/ols-2006-paper.pdf

If you've got any sort of serious disk array, ext3 is not the filesystem
to use....

> >>>How many folks are using these?  Any tuning tips?

Make sure you tell XFS the correct sunit/swidth. For hardware
raid5/6, sunit = per-disk chunksize, swidth = number of *data* disks in
array.

Cheers,

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