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Dynamic volume expansion query

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Regular Advisor

Dynamic volume expansion query

Hi Folks,

I am not able to find the information that I am looking for on any of the VMS websites that I know of, so, I'm turning on your experiences here or knowledge thereof:

1. Does DVE works on EMC SAN disks?
2. Per documentation, if I currently have this SAN disk of 9GB in size and I want to increase it to 18GB, what I'll need to do is:
a. to dismount my 9GB
b. increase it on the SAN side
c. mount it privately
d. do a set volume/limit
e. dismount it
f. mount it normally (i.e. /system, /cluster)

Now, if I need to increase the size of this disk in the future, all I need to do will be to execute a set volume /size=xxx DGAxxx, with no more need of dismounting it before doing a set volume/size, correct?
3. If my #2 statement above is correct, how is it done in a cluster then? Will the disk be automatically resized (if a previous set vol/limit has already been done successfull) once I do a set volume/size on one of the nodes?

Heinz W Genhart
Honored Contributor

Re: Dynamic volume expansion query

Hi Roose

We are using DVE on a XP12000 SAN without any problems

1. the existing disk must be mounted private and you have to do a set vol /LIMIT
2. The new (larger) disk must be initialized with qualifiers /LIMIT/SIZE=size-in-blocks-of-existing-disk
3. mount dsaxy/shad=(small-disk) label
4. mount dsaxy/shad=(small-disk, large-disk) label
5. Shadow copy
6. dismount small-disk
7. replace small disk with a new larger disk
8. init new large disk with /limit/size=size-in-blocks-of-replaced-old-disk
9. mount the new disk into the shadow set
10. wait for shadow copy finnished
11. do a set volume/size DSAxy

Hope that helps


Volker Halle
Honored Contributor

Re: Dynamic volume expansion query


AFAIK, you could skip your steps 2 and 8 (why init a disk, which will be the target of a shadow-copy ?).

OpenVMS Volume Shadowing has DDS (Dissimilar Device Shadowing), so it can cope with disks of different physical sizes.


DVE is an OpenVMS feature. If your EMC SAN disks can be increased in size with whatever management application on the EMC side, OpenVMS DVE will certainly work. You do not need to dismount the disk to increase it's physical size, but you need to just mount it privately ONCE to increase the Expansion Size Limit (typically to 1 TB) with SET VOL/LIMIT.

SET VOLUME/SIZE will force a mount-verification, which will cause an IO$_PACKACK QIO to obtain the new disk geometry and update the Total Blocks and the Logical Volume Size.

Occasional Visitor

Re: Dynamic volume expansion query

Hi Roose,

1. Does DVE works on EMC SAN disks?

Yes w've already extended our EMC SAN disks
with DVE.

Regular Advisor

Re: Dynamic volume expansion query

All, thanks for your reply.


Is it possible then to do a set vol/limit eventhough the SAN disk has not been increased yet? What I am coming up here is that let's say our current SAN disk is 9GB. Can I dismount it now, do a set vol/limit to basically "prepare" it for a future expansion? Then after this, just do an online volume expansion on the SAN side then a set vol/size? Or should it be dismount the disk first, increase the SAN disk, then do the set vol/limit, remount and finally, do a set vol/size?
Hein van den Heuvel
Honored Contributor

Re: Dynamic volume expansion query

I'm sure you can 'prepare', allowing you to pick the optimal time to temporarely mount the volume privately. The effect of the command is to rewrite [000000]bitmap.sys to match the new size, constraint by curent clusterzie and the 65K block max bitmap size.


Volker Halle
Honored Contributor

Re: Dynamic volume expansion query


yes - as Hein said - you can 'prepare' your disk volumes at any time, when you can mount them privately, to increase the Extension Limit to 1 TB. A limiting factor may be the current cluster size (as explained in $ HELP INIT/LIMIT) and the availability of enough contiguous space on the disk for allocating the required BITMAP.SYS file.

If you INIT new disks nowadays, it's suggested to always INIT them with /LIMIT.

Robert Gezelter
Honored Contributor

Re: Dynamic volume expansion query


Yes, setting /LIMIT before increasing the physical size is the best way to do things.

For a presentation on this, see my session from the 2005 HP Technology Forum, "Migrating OpenVMS Storage Environments without Interruption/Disruption". The notes are online at: http://www.rlgsc.com/hptechnologyforum/2005/1146.html

Volume migration in this fashion (e.g., using host based volume shadowing in conjunction with extendable volumes) allows migration between any physical devices supported by host based shadowing, without interruption of user activity.

I do recommend "straddling" three-member shadow sets during transitions, and care with startup/shutdown procedures.

- Bob Gezelter, http://www.rlgsc.com
Jan van den Ende
Honored Contributor

Re: Dynamic volume expansion query


if you have any use for experience stories:
we had our (3-member) savesets on HSZ80's.
For each set, we removed one member, copied-in on 3 new (SAN-)member; remove next member, copy-in another SAN; finaly 3rd member. Result migrated online to SAN config.
Our HSZ disks had already had the opportunity to set LIMIT earlier.
Storage need increased, we had our SAM people add some GB to the presented units.
SET VOLUME/SIZE (without value! ) and.. the newly presented space is available!
Like magic, real easy, in no time at all.



Have one on me.

Don't rust yours pelled jacker to fine doll missed aches.
Regular Advisor

Re: Dynamic volume expansion query

Thank you folks for answering my query. I will take note of the information you provided here and make some due deligence on my end before we do some implementation.