[Lustre-devel] WBC HLD outline
Alexander.Zarochentsev at Sun.COM
Wed Mar 25 09:17:29 PDT 2009
On 25 March 2009 11:33:12 Alex Zhuravlev wrote:
> >>>>> Alexander Zarochentsev (AZ) writes:
> AZ> On 24 March 2009 02:17:33 Robert Read wrote:
> >> Hi Zam,
> >> > MD update: a part of MD operation to be executed on one server,
> >> > contains one or more MDS/RAW operations.
> >> Why does the client need to to be more granular than an update?
> >> It seems MDS/Raw and update should be the same.
> AZ> well, better to say an update is MDS op if the operation touch
> only one AZ> MD server and MDS/Raw op in case of distributed
> I think this just adds unneeded entity to the system. stating that
> we either have updates or operations is simpler.
> >> Isn't this essentially what the cmm is doing today? (Breaking
> >> down distributed operations into per-node updates?) Are you
> >> expanding on Alex's idea of creating a new generic MD server
> >> stack?
> AZ> I just doubt that cmm code reuse is worth MD stack relayering.
> Can it be AZ> done as a subtask later?
> I don't think CMM is right thing because it essentially breaks
> layering: instead of sending object creation request in terms of OSD
> API or index insert in terms of OSD API it introduces some
> intermediate thing which is neither operation nor update.
Server MD stack has to support both WBC and non-WBC clients for the same
objects. It is why I think MDT layer should handle MD ops as well as
MDS/RAW ops. Then CMM only passes RAW operations to MDD layer, where
raw ops are already supported.
Alexander "Zam" Zarochentsev
Lustre Group, Sun Microsystems
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