[Lustre-devel] "Simple" HSM straw man
Peter.Braam at Sun.COM
Fri Oct 17 06:54:36 PDT 2008
On 10/17/08 3:47 AM, "Aurelien Degremont" <aurelien.degremont at cea.fr> wrote:
> 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 Is it interesting to have a file that is outdated and possibly
99.99% of (probably more 9's) backup systems do work this way, with
relatively little harm.
Also remember that many files are append only - for those it might be fine.
Philosophically it is a disaster of course. I would offer archiving of
files that are active, and in due course use snapshots.
>>> 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
>> 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
>>> done yet. If the data is changing, then the policy engine shouldn't
>>> have started a copyout process in the first place.
> 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.
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