zfs discuss - Dec 2009 - How to configure simple RAID-Z on OpenSolaris?

May be this question was already asked here, so I''m sorry for
redundancy.

What is a minimal amount of hard drives for enabling  RAID-Z on OpenSolaris? Is
it possible to have only 4 identical hard drives, and to install a whole system
on them with software RAID-Z underneath? Or enabling RAID-Z is possible only on
some additional 4 disks to the one from which the system boots?

Thanks.
-- 
This message posted from opensolaris.org

On Sun, 27 Dec 2009, Hillel Lubman wrote:
> May be this question was already asked here, so I''m sorry for
redundancy.
>
> What is a minimal amount of hard drives for enabling RAID-Z on 
> OpenSolaris? Is it possible to have only 4 identical hard drives, 
> and to install a whole system on them with software RAID-Z 
> underneath? Or enabling RAID-Z is possible only on some additional 4 
> disks to the one from which the system boots?
You can use as little as three drives for raidz but OpenSolaris can 
only boot from a single drive, or a mirror pair.  It can''t boot from 
raidz.  This means that you need to dedicate one or two drives (or 
partitions) for the root pool.  If you don''t mind losing some 
performance, you could use partitioning to put a 30GB partition on the 
first two drives, use that for a mirrored bootable root pool, and then 
use the remainder for a different pool with two "hog" partitions (from
first two disks) plus two drives in one raidz vdev.  This allows you 
to use raidz across all four drives, but losing 30GB from each drive, 
and using partitioning on the first two drives.

Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

Bob Friesenhahn wrote:
> OpenSolaris can only boot from a single drive, or a mirror pair. It
can''t boot from
> raidz. This means that you need to dedicate one or two drives (or
> partitions) for the root pool.
Thanks, that''s what I wanted to know. But why can''t
OpenSolaris boot from its own RAID-Z? Is it a GRUB related limitation? It would
make sense to be able to boot from RAID-Z if it''s such an integral part
of ZFS.

Regards,

Hillel.
-- 
This message posted from opensolaris.org

On Sun, 27 Dec 2009, Hillel Lubman wrote:
>
> Thanks, that''s what I wanted to know. But why can''t
OpenSolaris boot
> from its own RAID-Z? Is it a GRUB related limitation? It would make 
> sense to be able to boot from RAID-Z if it''s such an integral part
> of ZFS.
Yes, it is a GRUB limitation.  Anything put into GRUB becomes 
GPL-encumbered.  There is also the issue that GRUB can not communicate 
with the fault monitoring system (FMA) since it is not running yet, 
and GRUB is unlikely to be able to make correct recovery decisions for 
complex fault scenarios.  Keeping things simple improves system 
reliability.  I have heard that FreeBSD has a RAID-Z boot available.

Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/