[Evms-devel] Questions about shared volumes and devices

[Fabio C. <fa...@ne...>]

[ I sent this to cluster but probably here will be appropriate too...
sorry for double posting ]

Hi there,
 I have a couple of questions regarding the cluster features of EVMS. I
need to share 2x OCFS2 filesystems on 2 nodes, both mounted. OCFS2
provides the lock clustering. This is a mixed LVM2/EVMS environment
since the system partitions (root var etc) are created on top of LVM2
metadata directly managed by the OS. I could workaround any possible
issues just setting up the proper filters on /etc/lvm/lvm.conf so that
it won't find any EVMS volume, and the same has been done on /etc/evms.conf.

With EVMS I created a CSM container, called "shared" and on top of it I
created two different LVM2 volume groups.

Then I created an LVM2 volume on both VGs and on top of them I created
an EVMS volume for each. I don't know if this is the right practice,
since it's like adding a lot of metadata to the devices.. is it possible
to create EVMS volume on top of LVM2 Volume Groups? Seems not..

Anyway, now that I have my EVMS volumes I can run evms_activate on both
nodes, discover the devices and mount them. Everything is fine except...
 that I see several /dev/dm-* devices created by EVMS and I don't
understand why it happens. I used to create the EVMS volumes and all the
stuff on top of /dev/emcpower* devices so that I have an underlying
level that manages the multipath, but still EVMS generated /dev/md-* and
those are finally detected by OCFS2 (I can see it with mounted.ocfs2).

I'm thinking then to switch to multipath-tools and have DM that manages
multipath, and let EVMS create volumes on top of it. Could this solve
the confusion with OCFS2? I want the filesystem to rely on EVMS volumes
not on physical devices..

I also add below my sysfs_devices entry on evms.conf to give an idea how
I intend to manage the volumes:

        include = [ emcpower* ]
        exclude = [ sd* md* ]

Basically I exclude every device except the multipath ones. Now that I
intend to switch to DM Multipath-tools I think I will include just
"md-*"... but I don't know if I'm supposing good that EVMS will not
create any further DM device.

There's a lot of confusion in my head.. first of all if multipath can be
handled only by DM so that EVMS doesn't need to create further devices
or if this is a normal behavior of EVMS and I need to adjust my
evms.conf accordingly or using a different volume management scheme.

I hope that somebody will give a look at this email and give some
hints.. as far as I know not many people are brave to use those kind of
setups... ;)



Thanks,
Fabio