Presenting LUNs to VM Host for VM Guests

[N Ward]

We have a several LUNs presented to a VM Host for the VM Guests and want the guests to have more space.

Is it best to expand the single LUNs or present new LUNs which in turn will be presented to the VM Guests? I would guess the easiest is the first method.

My questions is, how does the VM Guest pick up the extra space that it now has?

[Torsten.]

This really depends on how the guest handles disks (what OS?).

[N Ward]

HPUX 11.23 on VM Host and VM Guests and Integrity 3.5 on 4 Guests and 2.0 on 2 others.

[Torsten.]

You have the choice - increase the disk size and use vgmodify on the guest or add a new disk to the LVM configuration.

[N Ward]

If a new LUN is presented to the VM Host, it requires presenting to the VM Guest manually. However if the existing SAN LUN is expanded the VM Guest can pick this up with vgmodify?

[melvyn burnard · Accepted solution]

If your VM Host is running HP-UX 11.23, you will need a reboot for it to pick up any extending done to LUN's presented to it.
It may just be easier to present new LUN's unless you can afford the downtime of a reboot.

[N Ward]

Thanks Melvyn (we have met before in Bristol), I was lead to believe that vgmodify would work to pick up the new space, without a reboot?

I haven't looked at this command in great detail just yet, but it appears to be able to increase the number of extents available following dynamic LUN size increases.

I believe it depends on the version of the Volume Group too. Version 2.0 is supported now, but version 1.0 only from Sept 2008 versions of HPUX 11.23.

[melvyn burnard]

to my knowledge, DOLE (Dynamic Online Lun Expansion) is only available on HP-UX 11.31.
With 11iv2 a reboot is still required to "read" the expansion on the LUN, but I will check.

[N Ward]

Much appreciated Melvyn, if thats the case, your suggestion of merely adding new LUNs will be our best approach as below.

The extra LUNs get presented to the VM Host I then present them to the VM Guest and no reboot for the Guest is required? Just an ioscan and insf -e?

[Kapil Jha]

Yes if it is 11.23 you will need to have a reboot for OS to recognise new LUN size.

Its better if you can add a new LUN unless you already you have lots of LUNs and want minimum LUNs to manager.

BR,
Kapil+

[melvyn burnard]

>>The extra LUNs get presented to the VM Host I then present them to the VM Guest and no reboot for the Guest is required? Just an ioscan and insf -e?

Yes, provided that adding these LUN's does NOT cause a new "scsi card" to be installed in the Guest machine.

[N Ward]

Thanks Melvyn, how can I check if this is likely to happen?

[melvyn burnard]

look at each VM in detail, and see what the current addresses are for each backing store. Remember that the VM sees each backing store as a SCSI disk, so when adding to a VM, unless you overide the configuration by supplying a bus/target setting (middle of the 5 fields in the syntax) then it starts with SCSI ID 0, and goes up to 6, 7 being the virtual scsi card if I recall. So check whether adding a further backing store may go higher than this, in which case it should "install" a new virtual scsi card which requires a reboot of the Guest to recognize it

[N Ward]

I've had a look at each VM and they all have one adapter present SCSI Id 0-7. It currently has 3 devices using it, leaving ids 4-7. spare, so I guess this should not be a problem.

[melvyn burnard]

correct. As long as you do not specify the optional fields, as in:
disk:scsi::disk:/dev/rdsk/cxtydz
Then it should just use the next address

[N Ward]

I have added the first LUN to the Guest and it has asked for a reboot, which I wasn't expecting.

"hpvmmodify: Unable to dynamically create device....... - Protocol error" then asks for a reboot.

Command used:

hpvmmodify -p1 -a disk:scsi::disk:/dev/rdsk/c20t0d5

[N Ward]

No-one experienced this before?

I was hoping given the configuration and the fact we had available slots on the VM that no reboot was required. This message seems to contradict that..

[Torsten.]

I have to check the manual again, but I guess this online feature starts with version 4.0.

[Torsten.]

The manual says (version 3.5 also):

All types of virtual storage devices can be added and removed dynamically fromvirtualmachines.
That is, virtual disks, virtual DVDs, tapes, media changers, and CD/DVD burners are all
hot-swappable.However, the virtual storage adapters are currently not hot-swappable. Therefore,
if all the virtual storage adapters are full, you must reboot the virtual machine when you add
additional devices.

[N Ward]

Thanks Torsten, RTFM I guess, but I did already have some knowledge about the adapters, hence I looked at the Guest first.

There is capacity so it should have taken the next available ids.. It doesn't make sense.. I will try and post the ioscan output for verification..

[N Ward]

Ok, I've managed to get downtime to reboot the Guest. What has happenned is a new card has been created on 0/0/0.

I added the disk as previously stated above leaving out the parameters for the scsi details. This was supposed to cause the Guest to be allocated the next available values as there were plenty on the card configured. Perhaps I can get round this problem because all the others are the same by dictating the values in advance rather than leaving it to the system..