Re: raid10,f2 Add a Controller: Which drives to move?

From: Neil Brown <neilb@suse.de>
To: Keld Simonsen <keld@keldix.com>
Cc: "Simon Matthews" <simon.d.matthews@gmail.com>,
	"Tomáš Dulík" <dulik@unart.cz>,
	st0ff@npl.de, "Linux RAID" <linux-raid@vger.kernel.org>
Subject: Re: raid10,f2 Add a Controller: Which drives to move?
Date: Tue, 13 Apr 2010 23:09:26 +1000	[thread overview]
Message-ID: <20100413230926.1273fc64@notabene.brown> (raw)
In-Reply-To: <20100413092354.GA7581@rap.rap.dk>

On Tue, 13 Apr 2010 11:23:54 +0200
Keld Simonsen <keld@keldix.com> wrote:

> I am not sure it has been said, but for a 4 disk raid10,f2 array
> you should place the first and the second disk on one controller, and then the 3rd
> and 4th on the second controller. Then you would have a copy of all blocks even
> if one controller fails.

Uhmm... no.

Disk:   1    2    3    4
blocks  a    b    c    d
        e    f    g    h
         .........
        d    a    b    c
        h    e    f    g

If you only have first and second, then block c is missing.
You want 1st and 3rd on one controller, 2nd and 4th on the other
Then either controller can access all blocks.

> 
> I believe the order is defined by the order the disks are specified in
> on the mdadm --create line.

Correct.

NeilBrown

> 
> best regards
> keld
> 
> On Mon, Apr 12, 2010 at 08:26:55PM -0700, Simon Matthews wrote:
> > 2010/4/12 Tomáš Dulík <dulik@unart.cz>:
> > > Stefan /*St0fF*/ Hübner napsal(a):
> > >>
> > >> I cannot quite understand your problem.  As every part of the array
> > >> contains it's own metadata, it doesn't matter to md which /dev/sdX a
> > >> drive is.  It might matter a bit for boot-time assembly, but actually
> > >> that's what UUIDs are for.
> > >>
> > >
> > > I know how UUIDs work.
> > > My problem with device names is not a "critical", it's about "user
> > > friendliness" of the physical disk management.
> > > If a disk fails and I receive email "A Fail event had been detected on md
> > > device /dev/md2. It could be related to component device /dev/sdd3", how
> > > will I know which disk should be replaced, if the device name is not
> > > fixed/persistent? I
> > 
> > Record the serial number of the disks and  which bay they are in.
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html