On 5/21/14 19:49 , wsnote wrote:
Hi,everyone!
I have 2 ceph clusters, one master zone, another secondary zone.
Now I have some question.
1. Can ceph have two or more secondary zones?
It's supposed to work, but I haven't tested it.
2. Can the role of master zone and secondary zone transform mutual?
I mean I can change the secondary zone to be master and the master
zone to secondary.
Yes and no. You can promote the slave to a master at any time by
disabling replication, and writing to it. You'll want to update your
region and zone maps, but that's only required to make replication
between zones work.
Converting the master to a secondary zone... I don't know. Everything
will work if you delete the contents of the old master, set it up as a
new secondary of the new master, and re-replicate everything. Nobody
wants to do that. It would be nice if you could just point the old
master (with it's existing data) at the new master, and it would start
replicating. I can't answer that.
3. How to deal with the situation when the master zone is down?
Now the secondary zone forbids all the operations of files, such as
create objects, delete objects.
When the master zone is down, users can't do anything to the files
except read objects from the secondary zone.
It's a bad user experience. Additionly, it will have a bad influence
on the confidence of the users.
I know the limit of secondary zone is out of consideration for the
consistency of data. However, is there another way to improve some
experience?
I think:
There can be a config that allow the files operations of the secondary
zone.If the master zone is down, the admin can enable it, then the
users can do files opeartions as usually. The secondary record all the
files operations of the files. When the master zone gets right, the
admin can sync files to the master zone manually.
The secondary zone tracks what metadata operations that it has replayed
from the master zone. It does this per bucket.
In theory, there's no reason you can have additional buckets in the
slave zone that the master zone doesn't have. Since these buckets
aren't replicated, there shouldn't be a problem writing to them. In
theory, you should even be able to write objects to the existing buckets
in the slave, as long as the master doesn't have those objects. I don't
know what would happen if you created one of those buckets or objects on
the master. Maybe replication breaks, or maybe it just overwrites the
data in the slave.
That's a lot of "in theory" though. I wouldn't attempt it without a lot
of simulation in test clusters.
--
*Craig Lewis*
Senior Systems Engineer
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Email cle...@centraldesktop.com <mailto:cle...@centraldesktop.com>
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