From: NeilBrown <neilb@suse.de>
To: "Jérôme Poulin" <jeromepoulin@gmail.com>
Cc: linux-raid <linux-raid@vger.kernel.org>
Subject: Re: Rotating RAID 1
Date: Tue, 23 Aug 2011 13:58:12 +1000 [thread overview]
Message-ID: <20110823135812.62c56cee@notabene.brown> (raw)
In-Reply-To: <CALJXSJqYXmvfoperm10XCLnGNA4WgMt_y7UoUSgPv3xjqScNcg@mail.gmail.com>
On Mon, 22 Aug 2011 23:45:53 -0400 Jérôme Poulin <jeromepoulin@gmail.com>
wrote:
> On Mon, Aug 15, 2011 at 7:55 PM, NeilBrown <neilb@suse.de> wrote:
> > Yes, add another one later would be difficult. But if you know up-front that
> > you will want three off-site devices it is easy.
> >
> > You could
> >
> > mdadm -C /dev/md0 -l1 -n2 -b internal /dev/A missing
> > mdadm -C /dev/md1 -l1 -n2 -b internal /dev/md0 missing
> > mdadm -C /dev/md2 -l1 -n2 -b internal /dev/md1 missing
> > mdadm -C /dev/md3 -l1 -n2 -b internal /dev/md2 missing
> >
> > mkfs /dev/md3 ; mount ..
> >
> > So you now have 4 "missing" devices.
>
> Alright, so I tried that on my project, being a low-end device is
> resulted in about 30-40% performance lost with 8 MDs (planning in
> advance), I tried disabling all bitmap to see if it helps and I get
> minimal performance gain. Is there anything I should tune in this
> case?
More concrete details would help...
So you have 8 MD RAID1s each with one missing device and the other device is
the next RAID1 down in the stack, except that last RAID1 where the one device
is a real device.
And in some unspecified test the RAID1 at the top of the stack gives 2/3 the
performance of the plain device? This the same when all bitmaps are
removed.
Certainly seems strange.
Can you give details of the test and numbers etc.
NeilBrown
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next prev parent reply other threads:[~2011-08-23 3:58 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-15 19:56 Rotating RAID 1 Jérôme Poulin
2011-08-15 20:19 ` Phil Turmel
2011-08-15 20:23 ` Jérôme Poulin
2011-08-15 20:21 ` Pavel Hofman
2011-08-15 20:25 ` Jérôme Poulin
2011-08-15 20:42 ` Pavel Hofman
2011-08-15 22:42 ` NeilBrown
2011-08-15 23:32 ` Jérôme Poulin
2011-08-15 23:55 ` NeilBrown
2011-08-16 6:34 ` Pavel Hofman
2011-09-09 22:28 ` Bill Davidsen
2011-09-11 19:21 ` Pavel Hofman
2011-09-12 14:20 ` Bill Davidsen
2011-08-23 3:45 ` Jérôme Poulin
2011-08-23 3:58 ` NeilBrown [this message]
2011-08-23 4:05 ` Jérôme Poulin
2011-08-24 2:28 ` Jérôme Poulin
2011-10-25 7:34 ` linbloke
2011-10-25 21:47 ` NeilBrown
2011-08-16 4:36 ` maurice
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