Operating System - OpenVMS
1830061 Members
2778 Online
109998 Solutions
New Discussion

Re: volume shadowing - disks with different maxfiles/cluster size

 
SOLVED
Go to solution
MarkOfAus
Valued Contributor

volume shadowing - disks with different maxfiles/cluster size

Hi all,
A question:

If volume shadowing 2 disks, each exactly the same physically but each has different maxfiles/cluster size, which does volume shadowing use?

set volume/limit explicitly states it uses init/cluster as its upper limit, but which, the lower of the two?

Thanks,
Mark
3 REPLIES 3
Andy Bustamante
Honored Contributor
Solution

Re: volume shadowing - disks with different maxfiles/cluster size

If the disks are the same size, your mount command(s) will determine which disk is over written. The maxfiles and clustersize from the source disk will replace values on the target disk.

Later versions of VMS support shadowing with disks of different size. This can be used to incease volume size "on the fly" without an outage, assuming the volume was initialized planning for growth.

Andy
If you don't have time to do it right, when will you have time to do it over? Reach me at first_name + "." + last_name at sysmanager net
John Gillings
Honored Contributor

Re: volume shadowing - disks with different maxfiles/cluster size

Mark,

>exactly the same physically but each has
>different maxfiles/cluster size, which
>does volume shadowing use?

In a shadowset, both disks are identical, so there can be no difference in maxfiles or cluster size.

Ideally you will have done:

$ INIT/SHADOW=(disk1,disk2)/CLUSTER=c/MAX=m/HEADERS=h etc..

prior to forming the shadowset, so the question is moot because everything will already be identical.

However, if you have taken 2 random disks and formed a shadow set:

$ MOUNT/SHADOW=(disk1,disk2) etc...

the shadowset is established with disk1, which is then shadow copied to disk2. All data and attributes of disk2 are overwritten with those of disk1. Since this has the potential to destroy data inadvertently, for safety, I'd recommend any shadowset mount have:

/POLICY=(REQUIRE_MEMBERS,VERIFY_LABEL)

VERIFY_LABEL prevents the wrong disk from being overwritten, and REQUIRE_MEMBERS requires that all devices be available, which prevents the shadow copy from being done in the wrong direction.
A crucible of informative mistakes
MarkOfAus
Valued Contributor

Re: volume shadowing - disks with different maxfiles/cluster size

Thanks.