[DRBD-user] Having Trouble with LVM on DRBD

Igor Cicimov icicimov at gmail.com
Sat Feb 27 07:28:46 CET 2016

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

On Sat, Feb 27, 2016 at 5:05 PM, Igor Cicimov <icicimov at gmail.com> wrote:

> On 27/02/2016 4:10 pm, "Eric Robinson" <eric.robinson at psmnv.com> wrote:
> >
> > > Can you please try following constraints instead the ones you have:
> >
> > > group g_drbd0 p_lvm_drbd0 p_fs_clust17 p_vip_clust17
> > > group g_drbd1 p_lvm_drbd1 p_fs_clust18 p_vip_clust18
> > > colocation c_clust17 inf: g_drbd0 ms_drbd0:Master
> > > colocation c_clust18 inf: g_drbd1 ms_drbd1:Master
> > > order o_clust17 inf: ms_drbd0:promote g_drbd0:start
> > > order o_clust18 inf: ms_drbd1:promote g_drbd1:start
> >
> > Those constraints seem to be working great. I can move the g_drbd0 and
> g_drbd1 resource groups freely back and forth between the nodes. However,
> this creates a problem for me because there will be a number of mysql
> resources on the servers (p_mysql_001, p_mysql_002, p_mysql_003,
> p_mysql_004, etc.).  In the past when I used resource groups, stopping any
> one mysql resource stopped all of the others, and removing one mysql
> resource from the group did the same thing. That's why I stopped using
> groups.
> >
> That's exactly what this configuration gives you right? Each group is
> collocated with one and only one drbd device on the master node.
Regarding starting/stopping of the resources tied up together in the same
group. I guess after adding MySQL the user case would be:

group g_drbd0 p_lvm_drbd0 p_fs_clust17 p_vip_clust17 p_mysql_001

Well all resources in the group are dedicated to the mysql resource so
stopping them together with mysql should not be of any issue at all. Apart
from the fact they have to be started again, the ip the lvm and the fs,
together with mysql which takes a second to get executed in case you are
concern about any latency. What's the purpose of those resources running
without their top mysql resource anyway?

However, if the mysql VIP in the group is being used by something else on
the server then yes you might have a problem with this. But as long as you
keep everything grouped and isolated I don't see what might go wrong.

> > I don't mind going back to using groups for the p_lvm, p_fs and p_vip
> resources, but the end result must be this: each of the mysql resources
> should be dependent on one of the g_drbd resource groups, but  independent
> of all the other mysql resources. What syntax should I use for that?
> >
> > And what was wrong with my constraints?
> You had left the Filesystem out of the picture. If you look carefully you
> will see that really the only difference between mine and yours
> constraints, apart from groups, is the filesystem primitives.
> Those work on my other clusters (but none of the others have LVM on drbd).
> >
> > --Eric
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