[Lustre-devel] "Simple" HSM straw man

[Aurelien Degremont <aurelien.degremont@cea.fr>]

Eric Barton a ?crit :
 > Partially purged files is a requirement to allow graphical file browsers
 > to retrieve icons from within the file.  It's OK to miss this out in the
 > first version, but it has to be there for the full product.

Think also of command like

$ file foo*

 >>> Is it interesting to have a file that is outdated and possibly
 >>> uncoherent?
 >> It is probably useful in some cases -- simulation checkpoints maybe.
 >
 > A corrupt simulation checkpoint is useless.  We _must_ provide a way to
 > ensure the HSM copy of a file is a known good snapshot.  We don't 
necessarily
 > have to abort the copyout if there is an update that could mean the
 > HSM copy would be corrupt since we can always just copy it out again,
 > but it doesn't seem hugely complicated to notify the backend, if not
 > the agent and let it decide.

Indeed, this is important

 >> I don't think we want to block the write just because the HSM copy 
isn't
 >> done yet.  If the data is changing, then the policy engine shouldn't
 >> have started a copyout process in the first place.
 >
 > Indeed.

You were speaking of a FS with only one big file and so we need to have 
a way to be sure it will be copied at least once, even if people are 
writting on it.
In this case, with a classical policy engine, this file will never be 
copied out because data is constantly changing.



-- 
Aurelien Degremont
CEA