[Lustre-devel] "Simple" HSM straw man
Aurelien Degremont
aurelien.degremont at cea.fr
Fri Oct 17 02:47:47 PDT 2008
Eric Barton a écrit :
> 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 Is it interesting to have a file that is outdated and possibly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
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