Same VG active on two machines?

[boje]

Hi!

Is it possible to have one VG active on two machines at the same time? I want to make two SG packages with access to the same LUN.

Br
Patrik

[Steven E. Protter · Accepted solution]

Shalom,

Yes if the volume group is on shared storage.

The vgchange command has -s parameter, see the man page to permit shared access.

Though the software you are using to actually access the volume group needs to be aware of this or there will be immediate data corruption.

Example Oracle server can not access data on a shared vg from two nodes without corruption.

Oracle RAC can.

SEP

[Duncan Edmonstone]

The *only* situation in which this is supported is when raw LV on the LUN is being used by Oracle RAC with Serviceguard extension for RAC (SGeRAC). In this situation you are using SLVM (shared LVM). Even then you wouldn't have 2 packages with access to the same LUN, you'd have a single multi-node package...

If you're thinking of sharing a *filesystem* between nodes, then you would need to look at a cluster filesystem, which somes as part of the Serviceguard Storage Management Suite:

http://www.hp.com/go/sgsms

But than runs the cluster filesystem over the clustered version of Veritas Volume manager, not LVM.

HTH

Duncan

[boje]

Hi and thx for your replies.

So if the VG are on EVA LUN it can not be used at the same time from two servers?
My experience of having a VG active on two machines at the same time is that the data will be corrupt.

Br
Patrik

[Matti_Kurkela]

If a LUN is accessed on two or more machines simultaneously, the data will be corrupted *unless* the machines are aware of each others and capable of cooperating.

For Oracle with raw LVs, the Oracle RAC has the necessary components for co-operation at the application level.

If the LUN contains a filesystem, you'll need a cluster-avare VxVM and a cluster-aware version of the vxfs filesystem, known as "Veritas CFS". The standard HP-UX LVM and basic vxfs (even with OnlineJFS) cannot do it.
These components are not free: contact HP sales to get price information.

NOTE: HP-UX 11.31 contains a Cache File System, also known as CFS. This is not the same as "Veritas CFS" clustered vxfs. This is an unfortunate acronym collision.

MK

[boje]

Hi again!

Thx for your answer.

Then it is not possible for me to do this. We use LVM and OnlineJFS.
To solve my problem i just need to make two packages with separate VG´s and duplicated data. But it is no problem with space.

Br
Patrik

[Steven E. Protter]

Shalom,

Your final approach is better.

Only way possible for two systems to be active on the same LUN at the same time is to activate the volume group in shared mode and run an application that is designed for this.

In this case, it is much better to simply have two LUNs and two volume groups.

You can for best performance make two applications active-passive with active/primary node being two different systems.

Don't forget to test fail over.

SEP

[Suraj K Sankari]

Hi,
Yes your approch is right.
for example if you have 2 packages and you get the best performance then make active each package into different box.

Suraj