On Sat, Jan 22, 2011 at 8:55 AM, Matthias Urlichs <matthias@xxxxxxxxxx> wrote:
> Hello ceph people,
>
> My situation is this: my Ceph cluster is distributed over multiple
> sites. The links between sites are rather slow. :-/
>
> Storing one copy of a file at each site should not be a problem with
> a reasonable crushmap, but ..:
>
> * how can I verify on which devices a file is stored?
>
> * is it possible to teach clients to read/write from "their", i.e.
> the local site's, copy of a file, instead of pulling stuff from
> a remote site? Or does ceph notice the speed difference by itself?
>
> * My crushmap looks like this:
> type 0 device
> type 1 host
> type 2 site
> type 3 root
> ... (root => 2 sites => 2 hosts each => 3 devices each)
> rule data {
> ruleset 0
> type replicated
> min_size 2
> max_size 2
> step take root
> step chooseleaf firstn 2 type site
> step emit
> }
>
> but when only one site is reachable, will there be one or tw
> copies of a file? If the former, how do I fix that? If the latter,
> will the copy be redistributed when (the link to) the second site
> comes back?
I've got the similar questions, using the above example, we'd have 2 x
(2x3) setup, ok.
- e.g., using with 2x replic, I'd see that each site storing the same
replicas (i.e., mirrored)
- but I'm unsure what would happen when one of the site goes down and later up.
- more, how's the objects stored in the remaining 2 hosts with 3osds each? (2x3)
I think there needs a multiple take or choose type to have a bit more
specific behaviors?
e.g., to further prevent the host loosing the 3osds worth of objects,
we do another 'step chooseleaf type host' ?
Thanks, DJ
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