Increasing Physical Volume size at the SAN level

[Adam Garsha]

After performing some web searches and scanning through the forums, I come to this conclusion:

With HP-UX (11.11), you can't increase LUN size at the SAN level and then propigate the changes through LVM to increase the size of a live/pre-existing filesystem (like you can on Tru64 and Windows); instead, you must create new LUNs and add them to the volume group and then extend the filesystem across the new LUN.

Can you confirm that this is correct?

i.e. that you must create new LUNs if you wish to have a larger filesystem (assuming no free space in the housing volume group or logical volume).

Also, do you know if this is something that is ear-marked for change in an upcoming version of HP-UX or LVM?

Much thanks,

--adam

[Steven E. Protter]

I have found this to be generally true on non-hp disk arrays.

I used to work with a Xiotech disk array and if we wanted to increase a lun we had to back up all the data on it, get it out of the volume and use pvcreate -f, set up a new logical volume and run newfs on it, followed by a data restore.

Once, in an unusual sequence of events, I succeeded in getting a LUN to expand. Though I took copies of the logs, I still can't see why it worked that one time.

Its a function of the fiber card drivers from HP and several years ago, I was promised an enhancement in this area that was never forthcoming.

I surmise it was a larger technical challenge than originally thought.

SEP

[Geoff Wild]

As far as I know, that is correct...either add new LUNS, or backup data, delete old LUNs...then create new ones with new size.

Though - I have never attempted what you are after...

We have always just added more LUNs to an existing VG.

Rgds...Geoff

[Devender Khatana]

Hi,

LUN Size expansion is supported in HP XP arrays . But LVM has no way of understanding it. It assumes and address only that size of LUN which was originally used for creating LVM structure.

I suppose it is not supported on HP-Ux. This is why we also add new LUNs and add them to existing VG's to extend or create file systems.

HTH,
Devender

[Florian Heigl (new acc)]

Adam,

unfortunately this is true.
Right now, I'd be against any experiments in that sector, also, most would prove unsuccessful, both because the kernel remembers the lun size somewhere (see various threads on diskinfo output after LUN resize) and because I really can't tell how LVM will handle a suddenly-larger PV.

hopefully this will change, but right now this is a big no-no.

[Vincente Fernandes]

Unfortunately that is how it is on HP-UX.
Also remember while doing that make sure the new LUN's size doesn't exceed the Max PE per PV otherwise the volume group will need to be removed and recreated to use all the size of the new bigger LUN's

[Devesh Pant_1]

We had a similar situtation where the volume group had to be rebuilt after taking a backup and then restoring after the volumegroup was created with the expanded LUN

thanks
Devesh

[Cem Tugrul]

Hi,
i have been usign Compaq EVA5000-Nase7000-
and some HP-ux srvs for 2 years and
i faced 3 times with this situation
and always HP recommended;

i-Take full bck
ii-export old Vg which includes LUNs from SAN
iii-Unpresent LUNs
iV-spmgr delete
v-Create new Lun and present it again
vi-Create vg-lv-FS
vii-Finally,go on with healty backup(restore)

After these steps,never Problem!
Good Luck,

[Adam Garsha]

Thanks all, here is what I got from HP CSS:

"LVM cannot handle a change in the size of an existing lun, To our knowledge there are no firm plans to implement this, though it has been talked about."

So, no firm plans to allow updated virtual disk at the SAN level and then propigating changes to filesystems. Too bad, it makes system management simpler.