[Gluster-users] New user, couple of questions (sharding+discard, arbiters, shutting down nodes)

[Krutika Dhananjay]

----- Original Message -----

> From: "Alan Hodgson" <ahodgson at simkin.ca>
> To: gluster-users at gluster.org
> Sent: Wednesday, October 28, 2015 11:22:24 PM
> Subject: [Gluster-users] New user, couple of questions (sharding+discard,
> arbiters, shutting down nodes)

> I have a couple of 2-node clusters I'm hoping to move from drbd+ocfs2 to
> glusterfs. I've been testing with 3.7.4 and I have a few questions.

> 1) I gather that 2-node replicas have quorum issues, and if you disable
> quorum, then they have split-brain issues. Do split-brains happen even if the
> network link is very reliable - I have point-to-point 10Gbit, and the only
> clients will be the brick servers? If so would it make more sense to make
> this
> a 4-node cluster and use arbiter volumes?

> 2) Sharding looks pretty good, as the volumes will be used exclusively for
> large VM backing images. I've been testing with 1GB shard sizes and
> performance seems good. It seems that sharded volumes don't support discard,
> though (ie. fstrim within VM guests). Is there a timeline on when that might
> be implemented?. Discard seems to work right on non-sharded volumes, but then
> heal times seem like they'll be an issue.
Thanks for the feedback, Alan. 

So 3.7.6 release is just two days away, and therefore it will not be possible to get discard implementation 
in by then. You can expect it to be available for 3.7.7 though (which would be end of Nov). 
Meanwhile, you can track its progress at https://bugzilla.redhat.com/show_bug.cgi?id=1261841 . 

-Krutika 

> 3) Is there operational documentation for maintenance procedures, like how to
> properly shut down nodes in a way that won't impact clients? What I got from
> a recent mailing list post suggests something like:

> killall glusterfs
> killall glusterfsd
> systemctl stop glusterd

> That seems to work in testing, the client VM's stay responsive. Is it safe?

> Thanks in advance for any advice.
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