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

[Neil Brown <neilb@suse.de>]

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.
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