incidentally what does the f2 layout do that it performs so much
better than the default?

Liam


On Thu, May 5, 2011 at 1:14 AM, Liam Kurmos [off-list ref] wrote:

Thanks guys!

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raid10: 220MB/s

Assuming the default 'n2' layout, I would expect 2*140 or 280, so this is a
little slow.  Try "--layout=f2" and see what you get (should be more like
RAID0).

mdadm -C /dev/md0 --level=raid10 --layout=f2 --raid-devices=4
/dev/sda1 /dev/sdc1 /dev/sdd1 /dev/sde1

dd if=/dev/md0 of=/dev/null bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 2.23352 s, 469 MB/s

:D

awesome!!

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raid5: ~165MB/s

I would expect 3*140 or 420, so this is very slow.  I wonder if read-ahead is
set badly.

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Can you:
  blockdev --getra /dev/md0
multiply the number it gives you by 8 and give it back with
  blockdev --setra NUMBER /dev/md0

genius.

im not really sure what this did but it totally fixed the problem.

look ahead was 768, set it 6144 and immediately got 400MB/s

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raid1: ~140MB/s  (single disk speed)

as expected.

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for 4 disks raid0 seems like suicide, but for my system drive the
speed advantage is so great im tempted to try it anyway and try and
use rsync to keep constant back up.

If you have somewhere to rsync to, then you have more disks so RAID10 might
be an answer... but I suspect you cannot move disks around that freely :-)

no need now! f2 layout is awesome.

many thanks,

Liam

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NeilBrown

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cheers for you responses,

Liam

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