From: "NeilBrown" <neilb@suse.de>
To: Tirumala Reddy Marri <tmarri@amcc.com>
Cc: linux-raid@vger.kernel.org
Subject: Re: writes raid-6 building
Date: Tue, 28 Jul 2009 16:48:07 +1000 (EST) [thread overview]
Message-ID: <ef22d815297edaa1b3c9a6507793ddcc.squirrel@neil.brown.name> (raw)
In-Reply-To: <AC5E1C3367E37D44970B81A6ADD1DA2C07C7D260@SDCEXCHANGE01.ad.amcc.com>
On Tue, July 28, 2009 11:09 am, Tirumala Reddy Marri wrote:
> While raid-6 is building I noticed writes are going on to all the
> drivers. Whereas in raid-5 I see writes happening to only one drive.
> Any clue ?
Because raid5 != raid6......
For raid5, mdadm creates a degraded array and recovers to a spare.
So it only writes to the spare.
For raid6, mdadm doesn't try to be so clever (the tradeoffs are difference)
and just creates a non-clean array so all the P and Q blocks get
written.
NeilBrown
>
> ---------- iostat dump for raid-6 ---
> Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
> sda 152.76 23.81 3.74 47 7
> sdb 181.91 25.35 5.50 50 10
> sdc 161.31 24.84 3.30 49 6
> sdd 153.77 23.52 4.02 46 8
> sde 169.85 26.29 3.27 52 6
> sdf 0.00 0.00 0.00 0 0
> sdg 0.00 0.00 0.00 0 0
> sdh 0.00 0.00 0.00 0 0
> sdi 0.00 0.00 0.00 0 0
>
> Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
> sda 152.02 24.05 3.44 47 6
> sdb 168.18 26.23 4.14 51 8
> sdc 163.64 22.76 3.69 45 7
> sdd 166.67 24.37 4.04 48 8
> sde 166.16 24.78 3.57 49 7
> sdf 0.00 0.00 0.00 0 0
> sdg 0.00 0.00 0.00 0 0
> sdh 0.00 0.00 0.00 0 0
> sdi 0.00 0.00 0.00 0 0
> ---------------
> Thanks,
> Marri
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prev parent reply other threads:[~2009-07-28 6:48 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-28 1:09 writes raid-6 building Tirumala Reddy Marri
2009-07-28 6:48 ` NeilBrown [this message]
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