[Lustre-discuss] MDS - RAID0 or RAID1

[Andreas Dilger]

On Jun 23, 2009  15:14 -0500, Carlos Santana wrote:
> What RAID level should be used for MDS configuration? The manual seems
> to suggest RAID1, however, the FAQ suggests RAID0 level.
> http://manual.lustre.org/manual/LustreManual16_HTML/RAID.html#50401396_pgfId-1290495
> http://wiki.lustre.org/index.php/Lustre_FAQ#What_is_the_typical_MDS_node_configuration.3F

The MDT should always use RAID-1.  If you need more space than will fit
on one disk, or you need more IOPS than can be handled by a single disk,
then create sufficient RAID-1 pairs for your needs and then stripe them
with RAID-0.  Having RAID-1 in pairs at the lower level minimizes the
chance that multiple disk failures will cause data loss.

I've clarified the FAQ in this regard.

> Also, is it possible to add more OSTs as the requirement grows?

Yes, adding new OSTs to an existing filesystem is a fairly common
procedure.  Note if you are planning on expanding your filesystem
in this way it makes sense to configure the MDT to have enough
space/inodes for the OSTs that will be added in the future.

> If yes, can additional resources be made part of RAID or can we
> turn existing non-RAID system into a RAID system? Any insights?

I'm not sure I understand this question.  OSTs should always use
RAID to avoid data loss, though RAID-5 or RAID-6 is OK for OSTs.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.