topic Re: Why we have activate the VGs in exclusive mode in MC/SG? in Operating System - HP-UX

Why we have activate the VGs in exclusive mode in MC/SG?

Lalo_Weng — Thu, 20 Sep 2001 14:36:54 GMT

Hi,

One question: In MC/SG, Why we have to activate the VGs in exclusive mode? What is the difference between share and exclusive mode? I need to know the detail.
Thanks in advance.

Re: Why we have activate the VGs in exclusive mode in MC/SG?

John Poff — Thu, 20 Sep 2001 14:38:29 GMT

Hello,

The VGs get activated in exclusive mode so that another node won't accidentally try to activate and mount the same VGs that another node is using.

JP

Re: Why we have activate the VGs in exclusive mode in MC/SG?

A. Clay Stephenson — Thu, 20 Sep 2001 14:42:33 GMT

Hi:

You definitely do not want more that one host to be altering a filesystem at a time - absolute chaos is assured. Shared mode is intended for the case where multiple hosts have the filesystem mounted read-only.

Re: Why we have activate the VGs in exclusive mode in MC/SG?

Santosh Nair_1 — Thu, 20 Sep 2001 14:44:00 GMT

You definitely do NOT want the VG activated in shared mode as this allows both nodes to activate VG which could potentially lead to data corruption.

-Santosh

Re: Why we have activate the VGs in exclusive mode in MC/SG?

James R. Ferguson — Thu, 20 Sep 2001 14:48:03 GMT

Hi Lalo:

Activation in "exclusive" mode is required so that only ONE operating system attempts read/write access to the disk. If this were not the case, you could not insure that either operating system would not overwrite the other's data or achieve any consistent view of in-memory data (not flushed to disk) vs. data written to disk!

Regards!

...JRF...

Re: Why we have activate the VGs in exclusive mode in MC/SG?

Sanjay_6 — Thu, 20 Sep 2001 15:07:58 GMT

Hi Lalo,

When the VG is added as a cluster VG in the Cluster configuration, the cluster control the VG. It makes the Vg cluster aware and depending on the pckage with which that Vg is associated, it gets activated on the node on which the package is started.

The VG is activated in exclusive mode so that at a time only one node is accessing that VG. Sort of a locking mechanish. You cannot lock one disk on two systems at a time. Hence the Vg gets activated on one node only and that node has exclusive access to that VG.

hope this helps.

thanks