Re: local mode -- a new tier mode

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On Thu, 17 Oct 2019 at 06:22, Lars Marowsky-Bree <lmb@xxxxxxxx> wrote:
>
> On 2019-10-16T11:28:25, " Honggang(Joseph) Yang " <eagle.rtlinux@xxxxxxxxx> wrote:
>
> I'm glad to see more performance work and caching happening in Ceph!
>
> I admit calling this a "tier" (to get the bike shedding done first ;-)
> is confusing me, because that used to mean something different. This
> seems to me to be more of a BlueStore feature based on hints/access from
> the upper layers?
>

User can explicitly send hint op or the do_op/agent send hint op based on object
access statistics to trigger a migration.

> So perhaps, at that level, it'd make sense to instead use the space on
> the RocksDB partition/device for this caching operation, instead of yet
> an additional device? (Intuitively, that's what most users already
> expect it does, anyway.)

yes, this is user friendly.

>
> How would this, compared to bcache, possibly handle situations where
> multiple OSDs share one caching device?
>

SSD is split into multiple partitions. Each partition is assigned  to
an osd as fast partitions.

> And does this only promote the local shard/replica? I'm wondering how
> this would affect EC pools.
>

yes, only promote the local shard/replica. But there is still some
work to do to support ec pool.

>
> Regards,
>     Lars
>
> --
> SUSE Linux GmbH, GF: Felix Imendörffer, Mary Higgins, Sri Rasiah, HRB 21284 (AG Nürnberg)
> "Architects should open possibilities and not determine everything." (Ueli Zbinden)




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