VG & PV in a cluster environment

[abcd7]

Hi,

If a VG is not marked as sharable ( vgchange -S), can't it be accessed by more than a node in an HA environment ? Its already maked as cluster aware .


If a disk is added to a cluser aware VG, and the LVOL is extended, can we just do a 'vgextend' on the adoptive nodes, bypassing the usual procedure of making a map file from the primary node and exporting & imporing this VG on the adoptive nodes ?


Thanks

Doug

[Stephen Doud · Accepted solution]

2 questions, 2 answers...

1) HPUX does not have a back channel to communicate inode changes to other HPUX kernels. Therefore, no matter how you manage to activate a VG on multiple servers at the same time, updating a file or file system on one node will not be communicated to the other servers' in-core inode table. That means the node that didn't make the change will perceive a corrupt file system when it notes a difference between in-core inode table structures and on-disk structures - and will likely reboot (panic).
In summary - if you really need a cluster file system, investigate the Serviceguard Storage Management Suite, which uses a back-channel to communicate such changes.

2) vgextend increments the PV count in the LVM metadata on-disk (VGRA). So if you vgextend the disk twice (once on each node), the PV count will be inaccurate (larger than actual number of disks in the VG).

The appropriate method to update lvmtab on nodes where the vgextend did NOT take place is to vgexport and then vgimport the volume group, and include the new disk in the process.

For HA environments, the procedure is fairly well documented both in the ITRC forum AND in the Managing Serviceguard manual.

[abcd7]

Hi Stepen,

Thank you so much. I am quite OK with the answer for 2nd question.

But dear me, am not convinced with the first one :-)

What I want to know is the use of 'sharable' option for a VG.

I have been using SG for quite sometime, but never used 'sharable' option. All I used to do was mark it cluster aware and use it. It works without any issue. Its an Active - Standby envirionment and at any time only one node activates it in exclusive mode. I am wondering if I missed this Sharable option ...

Thanks

Doug

[Stephen Doud]

Shared activation mode is only enabled when SGeRAC is installed, and is only intended for use with raw volume access (as used by Oracle). It cannot be used for any other purpose.

[abcd7]

Hi Stephen,

Thank you very much.

Have a nice weekend.

Cheers

Doug