[DRBD-user] Parallel resource startup, scalability questions

Arnold Krille arnold at arnoldarts.de
Wed Jul 3 22:44:11 CEST 2013

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


On Wed, 3 Jul 2013 14:31:40 +0900 Christian Balzer <chibi at gol.com>
> On Tue, 2 Jul 2013 22:15:06 +0200 Arnold Krille wrote:
> > On Tue, 2 Jul 2013 17:08:30 +0900 Christian Balzer <chibi at gol.com>
> > wrote:
> > I don't have 30 vms, more like 15. But at least one drbd-volume for
> > each machine. And dependencies defined so the ldap-server has to be
> > up before the others start that need it.
> > 
> > And using individual drbd-resources for the machines might be a bit
> > more to set-up when doing it all at once (my setup has grown over
> > time), it allows to distribute the vms on the two nodes, so the vms
> > don't need to run all on one node. And when you also define scores
> > for importance, you can over-commit the memory (and cpu) of the two
> > nodes so that normally everything runs and only in case of a
> > node-failure some not so importent vms are stopped/not started.
> >
> That's something I was planning to do up to a point.
> I wonder what you're using to manage/create the VMs, the LCMC GUI is
> a bit limited compared to virt-manager or Proxmox when it comes to
> details like CPU pinning, which I will need.

I am pretty old-school (hey, I am over thirty). I use the commandline
and vim to define pacemaker-resources and virtual machines.
LCMC might be fast for a java-based gui app, but it still has the
penalty of a java gui app, at least on our linux terminal server it
wasn't usable when we tried 1.5 years ago. And virt-manager on debian
squeeze tends to "hide" some of the newer features of libvirt...

The cluster-nodes all have a dir /root/machines that holds the
xml-files for the nodes. This dir is synced with csync2 with a
post-sync action to run "virsh define <file>" on the remote machine.
Its assumed that one modifies the local file, then does "virsh define
<file>" locally and if it works "csync2 -x".

My collegues use virt-manager to see if machines still work and have
learned that some machines shouldn't be started manually unless the
cluster gives them explicit permission to do so...

> OTOH one can always put the config directory onto an OCFS2 device and
> use whatever tool is best w/o having to worry about cluster-wide
> replication. 

I had a very funny week while I tried to use OCFS2 in production.
Thanks, but no thanks.

I might be tempted to switch the config-managment for the
machine-definition to chef, but I don't yet know how that would
integrate with our setup with pacemaker and stuff. And you wouldn't
want a terminal-server-vm to reboot during office hours just because
chef detected a change in a config-file...

Have fun,

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