Volume Group read-only mode

[Ivan Efimenko]

We have cluster with two nodes.
VG has been activated with vgchange -a y from node1 and with vgchange -a r (read-only mode) from node2. Changes made from node1 since that to files in file system residing in this VG are not effective (or just visible?) from node2.
Is it right? Or the problem is in absence of some patches?

[Andre Machado_1]

Hi,

When you work with Cluster you use the vgchange -a e, not -a y.
-a e option is exclusive mode.

Work?s with the VG activate in two machines
is only possible with the LockManager Software,
this software work?s with MC/ServiceGuard.

When you active the volume goup, is write in VGSA, and if other machi try to activate the volume group the "Conflicts Mode Activate" is reposted.

[Emil Velez · Accepted solution]

The problem is that the file system structures are read at mount time. SO if you add a file to the filesystem from the read/write side the read only side does not see it.

Read only activation was not meant for this. You should have 2 different logical volumes 1 being used Read/write on the node that has the volume group vgchange -a y. Another logical volume mounted read only from the system that has the volume group vgchange -a r

Many people use this as a way to split a mirrored logical volume and mount the split off copy read only on another system so it can be backed up.

If you want another system to see a filesystem use NFS.

I hope this clears up some of the vgchange -a r questions.

[Anonymous]

just to make sure that you're aware of this...
With MC/SG,
pkg01
on nodeA (ie vg01 "-a e") AND
on nodeB same vg01 "-a r"

will give you problems if nodeA fails
as SG cannot start pkg01 on nodeB as long as it is read-only-activated (ie needs a "-a n" first).

So as "-a r" is a kind of "jumping on thin ice" I always try to keep this time to a minimum level.

take care, thomas.