I have a replica volume created as:
gluster volume create vol1 replica 4 \
host{1,2,3,4}:/mnt/gluster/brick1/data \
force
All hosts host{1,2,3,4} mount this volume as:
localhost:/vol1 /mnt/gluster/vol1 glusterfs defaults
Some other hosts are trusted peers but do not contribute bricks, and they
also mount vol1 in the same way:
localhost:/vol1 /mnt/gluster/vol1 glusterfs defaults
All hosts run CentOS 7.9, and all are running glusterfs 9.4 or 9.5 from
centos-release-gluster9-1.0-1.el7.noarch.
All hosts run kvm guests that use qcow2 files for root filesystems that
are stored on gluster volume vol1.
This is all working well, as long as none of host{1,2,3,4} go offline.
I want to take one of host{1,2,3,4} offline temporarily for maintenance.
I'll refer to this as hostX.
I understand that hostX will need to be healed when it comes back online.
I would, of course, migrate guests from hostX to another host, in which
case hostX would then only be participating as a gluster replica brick
provider and serving gluster client requests.
What I've experienced is that if I take one of host{1,2,3,4} offline, this
can disrupt some of the VM guests on various other hosts such that their
root filesystems go to read-only.
What I'm looking for here are suggestions as to how to properly take one
of host{1,2,3,4} offline to avoid such disruption or how to tune the
libvirt kvm hosts and guests to be sufficiently resilient in the face of
taking one gluster replica node offline.
Thanks,
Todd
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