[Lustre-devel] How store HSM metadata in MDT ?

[Peter Braam <Peter.Braam@Sun.COM>]

On 7/4/08 8:37 AM, "Aurelien Degremont" <aurelien.degremont@cea.fr> wrote:

> Peter Braam a ?crit :
>> If there is more than one copy in the archive, it would be preferable if the
>> archive could maintain a mapping from the Lustre fid of the file to the
>> archived copies.  Associated with the FID of the data would then be a list
>> of archived copies, timestamps etc.
> 
> Do you mean that the HSM will be aware of various versions of one same
> file, identified in Lustre by a FID ?
> Or this will be masked by the archiving tool , doing some tricks to
> simulate it ?
> 
>> Can that be done in HPSS?
> 
> HPSS alone cannot do versioning on its files presently.

But your archiving utility that copies from Lustre to HPSS can maintain
database of these objects - no need to store anything in Lustre.


> 
> 
>> If not, policy related operations like purging older files etc will become
>> very complex and not scalable.  For example, a search to find older files in
>> the archive would require an e2scan operation to find the inodes and then
>> the objects in the archive.  If the file system was not available anymore
>> (for whatever reason), it is not even clear that such a purge could still
>> happen.
>> 
>> With an archive based database this can be an indexed search in the archive,
>> which is faster and more appropriate.
> 
> By purgin do mean purging in Lustre or in the HSM?

The HSM.

> There's no issue with purging in Lustre because this do not imply the HSM.
> And removal of oldest copies in the HSM could be done asynchronously,
> slowly.

There is a rule in Lustre - no scanning, ever.  This rule will not be broken
by HSM.  

So, you have to move your management of ID's of the archvied copies outside
of Lustre, in some database.  This will actually save you time - doing this
in the MDS will be no fun.

The MDS should only get attributes to indicate if and what version of a file
is in the archive and a cursor (maybe other information) in relation with
ongoing restores.

Peter


> 
> I'm not sure I see what you mean here
>