On 05/01/2017 11:55 AM, Pranith Kumar Karampuri wrote:
On Tue, May 2, 2017 at 12:20 AM, Gandalf Corvotempesta
<[email protected]
<mailto:[email protected]>> wrote:
2017-05-01 20:43 GMT+02:00 Shyam <[email protected]
<mailto:[email protected]>>:
> I do agree that for the duration a brick is replaced its
replication count
> is down by 1, is that your concern? In which case I do note that
without (a)
> above, availability is at risk during the operation. Which needs
other
> strategies/changes to ensure tolerance to errors/faults.
Oh, yes, i've forgot this too.
I don't know Ceph, but Lizard, when moving chunks across the cluster,
does a copy, not a movement
During the whole operation you'll end with some files/chunks
replicated more than the requirement.
Replace-brick as a command is implemented with the goal of replacing a
disk that went bad. So the availability was already less. In 2013-2014
I proposed that we do it by adding brick to just the replica set and
increase its replica-count just for that set once heal is complete we
could remove this brick. But at the point I didn't see any benefit to
that approach, because availability was already down by 1. But with
all of this discussion it seems like a good time to revive this idea.
I saw that Shyam suggested the same in the PR he mentioned before.
I've always been against the idea of being a replica down based on that
supposition. I've never had to replace-brick because a brick failed.
It's always been for reconfiguration reasons. Good monitoring and
analysis can predict drive failures in plenty of time to replace a
functioning brick.
If you have a replica 3, during the movement, some file get replica 4
In Gluster the same operation will bring you replica 2.
IMHO, this isn't a viable/reliable solution
Any change to change "replace-brick" to increase the replica count
during the operation ?
It can be done. We just need to find time to do this.
--
Pranith
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