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Volume size limitation on OpenVMS 7.3

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fred mudgett_2
Occasional Advisor

Volume size limitation on OpenVMS 7.3

Greetings, we have a customer with a new EVA which he wants to make a 4TB volume accessable from a system running Openvms 7.3. I've checked the SPD and could find no limitations mentioned there but did see a indication that there is a 1TB size limitation on OpenVMS volumes.

Any direction would be appreciated.
7 REPLIES
Hein van den Heuvel
Honored Contributor
Solution

Re: Volume size limitation on OpenVMS 7.3

>> he wants to make a 4TB volume accessable from a system running Openvms 7.3

He may want all he like, but it ain't going to happen.

1TB is the limit.

Think about it!

OpenVMS address all (512 byte) disk blocks using 32-bit pointers. That would suggest an absolute max of 2TB. But nobody trusts the 'signed versus unsigned' implications of using that last bit. Thus the 1TB limit (2*31 * 512) was born.

You could actually combine multiple 1TB units into a single bound volume set, giving the appearance of a 4TB device.
That would be legal, and transparent, but a silly thing to do.

Please question the customer WHY they think a a single volume is preferrable and HOW they intend to provide backups and disaster recovery for such large blob of data.

Multiple smaller, but still big, volumes give much better visibiltiy and opportunities for tuning an parallisme with just a small increment in management overhead.

Good Luck!

Hein.
Robert Gezelter
Honored Contributor

Re: Volume size limitation on OpenVMS 7.3

Fred,

I agree with Hein's analysis, except for the comment:

"That would be legal, and transparent, but a silly thing to do."

Volume sets may be out of fashion, but they are a useful tool. I do agreen with Hein's comment about backup/restore operational issues.

I can conceive of situations where I would use this approach, but they would be highly specific to the individual site.

- Bob Gezelter, http://www.rlgsc.com
Robert Brooks_1
Honored Contributor

Re: Volume size limitation on OpenVMS 7.3

Is the version really V7.3, as opposed to V7.3-1 or V7.3-2?

V7.3 is quite ancient (and buggy!) with respect to fibre channel and multipath.

V7.3-2, while no longer on standard support, does have much better-performing SCSI and fibre channel storage, if one installs the latest patch kits.

If this site is using host-based volume shadowing, using V7.3-2 is almost a must.

-- Rob
Rob Leadbeater
Honored Contributor

Re: Volume size limitation on OpenVMS 7.3

Hi Fred,

Another thing to throw into the pot is that current EVAs can create a LUN with a maximum size of 2TB...

Cheers,

Rob
Karl Rohwedder
Honored Contributor

Re: Volume size limitation on OpenVMS 7.3

During the current TUD Andy G. mentioned, that a version after V8.4 may lift this restriction to 2TB.

regards Kalle
Karl Rohwedder
Honored Contributor

Re: Volume size limitation on OpenVMS 7.3

Sorry, typo: after V8.3 of course...

regards Kalle
fred mudgett_2
Occasional Advisor

Re: Volume size limitation on OpenVMS 7.3

Thank You all very much.