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

[Alan Hodgson]

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.

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.