Le Ven 26 juin 2015, à 00:01, James (Fei) Liu-SSI a écrit :
> Hi Cephers,
> It is not easy to ask when Ceph is going to support inline
> dedup/compression across OSDs in RADOS.
disclamer: I am not a Cepher.
This would mean some kind of distributed key value store that is fast
enough
to deliver one query by written object or a kind of distributed in ram
lru hash
table in order to optimistically identify the hottest objects.
(The one that are identical and get written the most often)
I am more used to block devices so I don't realise how many different
objects
per second get written on disk on a ceph setup.
I don't see how it would cope with partial writes.
If you need speed like in a block device setup you can forget anything
B-TREE to
implement the key-value store because it's O(log n).
So you are left with solutions like SILT that will eat some RAM and beg
you
for an SSD in exchange of O(1+Epsilon) lookups.(Probably good for
Samsung ;)
See https://www.cs.cmu.edu/~dga/papers/silt-sosp2011.pdf
>From my experience with block device setup deduplication is very
demanding to
the key/value store. Maybe with only complete write on big objects this
problem
would disappear.
Best regards
Benoît
> because it is not easy task
> and answered. Ceph is providing replication and EC for performance
> and failure recovery. But we also lose the efficiency of storage
> store and cost associate with it. It is kind of contradicted with
> each other. But I am curious how other Cephers think about this
> question.
> Any plan for Cephers to do anything regarding to inline
> dedupe/compression except the features brought by local node itself
> like BRTFS?
>
> Regards,
> James
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