Re: Help with low raid5 performance

[Peter Kerwien <peter%kerwien.homeip.net@localhost>]

On Mon, 15 Nov 2010 12:11:08 +0000, Ian Clark <mrrooster%gmail.com@localhost> 
wrote:
> On 12 November 2010 22:14, Peter Kerwien <peter%kerwien.homeip.net@localhost> 
> wrote:
> > Any comments on the following:
> >
> > Same disks, HW but different OS and filesystem: Linux Mint 10 
> > (amd64)
> > with mdadm created raid-5 and ext4. Chunk size = 32KB, block size = 
> > 4KB,
> > stride size = 8 blocks = 32KB.
> >
> > # dd if=/mnt/vol1/pub/foo.mkv of=/dev/null bs=100M count=100
> > 100+0 records in
> > 100+0 records out
> > 10485760000 bytes (10 GB) copied, 100.641 s, 104 MB/s
> >
> > # dd if=/dev/zero of=/mnt/vol1/pub/zero bs=100M count=100
> > 100+0 records in
> > 100+0 records out
> > 10485760000 bytes (10 GB) copied, 102.646 s, 102 MB/s
> >
> > Note the *slightly* higher write speed. Comments?
> I've noticed that with the same RAID configuration as yourself, I
> started the wedge at 128 sectors, not 64 (ie a whole stripe of data
> from the start), I remember having terrible performance until I got
> this bit correct.

Interesting! So just moving the wedge a whole stripe was the trick?

BR,

/Peter

> I have 3x2T HGST disks, set up like the following:-
>
> (ian:~)$ sudo raidctl -G raid0
> # raidctl config file for /dev/rraid0d


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