Re: Fastest Chunk Size w/XFS For MD Software RAID = 1024k

[David Chinner <dgc@xxxxxxx>]

On Thu, Jun 28, 2007 at 04:27:15AM -0400, Justin Piszcz wrote:
> 
> 
> On Thu, 28 Jun 2007, Peter Rabbitson wrote:
> 
> >Justin Piszcz wrote:
> >>mdadm --create \
> >>      --verbose /dev/md3 \
> >>      --level=5 \
> >>      --raid-devices=10 \
> >>      --chunk=1024 \
> >>      --force \
> >>      --run
> >>      /dev/sd[cdefghijkl]1
> >>
> >>Justin.
> >
> >Interesting, I came up with the same results (1M chunk being superior) 
> >with a completely different raid set with XFS on top:
> >
> >mdadm        --create \
> >     --level=10 \
> >     --chunk=1024 \
> >     --raid-devices=4 \
> >     --layout=f3 \
> >     ...
> >
> >Could it be attributed to XFS itself?

More likely it's related to the I/O size being sent to the disks. The larger
the chunk size, the larger the I/o hitting each disk. I think the maximum I/O
size is 512k ATM on x86(_64), so a chunk of 1MB will guarantee that there are
maximally sized I/Os being sent to the disk....

Cheers,

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