Do I need serviceguard to vgexport/inport from one box to another?

[Steve Post]

Currently we have two Vclass boxes (hpux11.0) sharing disks on an EMC disk array.
If production would fail, the prodbox would not be using vgprod. So we would activate vgprod on the test box. Even though the device names of the disks are different between the prod and test box, the disks are the same.

Before any failure, I would do this to test failover capability...
on prodbox: vgexport -s -m /tmp/vgprod.map -p /dev/vgprod
copy prodbox:/tmp/vgprod.map to testbox:/tmp/vgprod.map
on prodbox: vgchange -a n /dev/vgprod
on testbox: make the vgprod directory and the group file.
on testbox: vgimport -s -m /tmp/vgprod.map
on testbox: vgchange -a y vgprod

Now let me ASSUME the -s command is not available if I don't have MC/Service Guard. Here's the same stuff with that "-s".
on prodbox: vgexport -m /tmp/vgprod.map -p /dev/vgprod
on prodbox: vgdisplay -v /dev/vgprod
copy prodbox:/tmp/vgprod.map to testbox:/tmp/vgprod.map
By hand, identify the disks on the testbox that correspond to vgprod on the prodbox.
on prodbox: vgchange -a n /dev/vgprod
on testbox: make the vgprod directory and the group file.
on testbox: vgimport -m /tmp/vgprod.map /dev/dsk/cXtYdZ /dev/dsk/cXtYdZ....
on testbox: vgchange -a y vgprod

Currently, disk 1 on prodbox c10t3d0 is testbox c2t4d0, disk 2 on ...etc, etc.

We are looking at getting two rx4640 servers (11i) both hooked to an EVA4000 san array. The new servers and san array are not here. They're not even bought yet. I have never used a san array before. But I expect my new prodbox and testbox will be able to see the same disks.

When I stated this to the seller I was told that I do not want the testbox to see the disks of vgprod, because I might accidentally use the vgprod disks on the testbox while they are in use. But if I follow that advice, I can't have the failover of vgprod to the testbox.

So...we finally come to my question:
Can I have the testbox see the production disks (aka vgprod)?
Why is this a bad idea?

[Geoff Wild]

No you don't need serviceguard to do that.

We do that all the time - to our backup server.

On our prod boxes (which happen to be MC/SG), we utilize a 3rd mirror (BCV on EMC) - that prod doesn't see - and mount that on the backup server.

For QA systems, we mount the exact same disks on the backup server (after unmounting, vgchanging from QA server).

Rgds...Geoff

[baiju_3 · Accepted solution]

If you do not have LUN Masking product enabled on the disk array . eny host on SAN can see any lun . The risk being system administrator doing a pvcreate -f on LUNs thinking it is free on that server but may be in use on some other .

Since in your case the number of servers are less , you can manage easly with out using masking .

And the steps you given are absolutely correct , but you may add a preview option to vgimport command to make sure every thing is alright before doing the actual import .

and note ,all the export /import command will have the vgname as parameter at the end .

Thanks,
BL.

[baiju_3]

Yes Geff is right , for -s option service gurad is not must .


thx,
bl.

[Howard Marshall]

As stated before you can do this with no problem I just have one piece of advice.

If your prod machine goes down, you can't get a current map and disk drive list for the import command on the backup machine. It may be a good idea to periodically record that information, say using the vgexport with the -p option on the prod server and copying it over the backup server so you have it there if you need it. Just one thing, if you use the -f option you will need to make sure the disks have the same name on both machines or include a script to convert them.

H

[Steve Post]

I run the "vgexport -m /tmp/vgprod.map -s -p -v /dev/vgprod" each month and also when I make a change to the volume group.

I keep the map on the failover box. But I also move it to my pc, and burn it to CDROM (along with lots of other sysadm information and documents on disaster recovery). I also have some of the key information in hard copy for fast reference.

Like a typical systems administrator, I'm paranoid about losing the systems for a long duration. I would really hate it to find that new hardware removes the ability for me to get stuff going again.

[Devender Khatana]

Hi,

All options of vgimport are available within default LVM itself. Service Guard does not add anything to it including shared mode.

As far as the sharing disks on two nodes is concerned, it is not at all a bad idea but precaution should be taken while handling shared disks, as try to mount file systems of one VG on two nodes simultaneously may lead to data corruption in those file systems.

HTH,
Devender