--- On Fri, 5/2/08, George Spelvin <linux@horizon.com> wrote:

From: George Spelvin <redacted>
Subject: Re: Sharing disks amoung multiple software RAIDs
To: alex14641@yahoo.com
Cc: linux@horizon.com, linux-raid@vger.kernel.org
Date: Friday, May 2, 2008, 4:36 AM
Can you explain what you mean, exactly?

As an example, you have disks /dev/sd[abc]. /dev/md0 would be made 
from /dev/sda1, /dev/sdb1, and /dev/sdc1; /dev/md1 would be made  from /dev/sda2, /dev/sdb2, and /dev/sdc2.

Do you just mean having two partitions on the same drive
used as part
of other RAID arrays?  That works fine.
Having two heavilty used partitions on the same drive
causes some
performance issues, 

In this case they are heavily used.

but no correctness ones.  And
there's nothing
special about RAID for this consideration; it would apply
with
non-RAID partitions as well.

But I have mirrored swap striped across all drives; I
don't
use swap a lot and it's not worth getting dedicated
drives.

Likewise, /boot is a 6-way RAID-1 emergency rescue
partition.
I can boot off any drive, and I have a basic text-mode
install
with all the disaster recovery tools.  Again, not heavily
used.

If you're doing serious database work, it's common
to split the
system, log, and database across different spindles.  But
that's
independent of whether RAID is used for any of them.


But there are other possible interpretations of
"sharing among multiple
RAIDs", like hot spares and the like.  Could you be
more specific?
Obviously, having the same partition active in multiple
different
arrays would be an unmitigated disaster, but I don't
think you mean that.
(And I don't think mdadm lets you do it, either.)

One thing that's very nice about Linux software RAID is
that you *don't*
have to RAID whole drives.  It took me a while to
understand Intel's
"Matrix RAID" feature because it had never
occurred to me that a RAID
array *couldn't* be set up that way.

      ____________________________________________________________________________________
Be a better friend, newshound, and 
know-it-all with Yahoo! Mobile.  Try it now.  http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ