Lustre discuss - Mar 2011 - mixed oss/ost performance question

I have a general question about mixing of osts with slower or faster backing
storage.
we have a fair number of slower "legacy" disk pools and a bunch of
newer faster ones.
the fast and slow are aggregated separately to provide OST storage targets with
a uniform speed characteristic (slow or fast),

my question is whether it would be better to make two separate filesystems (say
lustre1 and lustre2) with the slow and fast OSTs respectively,
or is it reasonable to have these all under one filesystem.

sam aparicio

On 2011-03-04, at 3:14 PM, Samuel Aparicio wrote:
> I have a general question about mixing of osts with slower or faster
backing storage.  we have a fair number of slower "legacy" disk pools
and a bunch of newer faster ones.  the fast and slow are aggregated separately
to provide OST storage targets with a uniform speed characteristic (slow or
fast),
> 
> my question is whether it would be better to make two separate filesystems
(say lustre1 and lustre2) with the slow and fast OSTs respectively,
> or is it reasonable to have these all under one filesystem.
It depends today on the sophistication of your users.  It is possible to split
different storage classes with OST pools (see the commands "lctl
pool_add" and
"lfs setstripe -p"), but these are "optional" separations
today.  If users don''t specify any pool then the default is to use all
OSTs (mixing fast and slow storage).  You CAN specify default pools on a
per-directory basis, but this only applies to newly-created files.

Cheers, Andreas
--
Andreas Dilger 
Principal Engineer
Whamcloud, Inc.