[Info-vax] ODS-5 to ODS-2 Data Migration

[Michael Moroney]

"Zane H. Healy" <healyzh at avanthar.avanthar.com> writes:

>Bob Gezelter <gezelter at rlgsc.com> wrote:

>> A better question is: Why is it desired to revert to ODS-2?

>These is for my home system.  I'm moving as much of my VMS data and apps
>back to VAX as I can, and then creating a SIMH VAX cluster.  The desired
>goal is less dependance on hardware that's in the 18 year range, and a much
>lower power bill.

Beware, there was a change to ODS-2 that isn't compatible with
VMS V7.2 and earlier (or was it V7.1 and earlier?). There's no version
bump with this change, either.  Older versions of VMS won't be able to
mount these disks.  The biggest change was the size of the allocation
bitmap, from 255 blocks (thus a maximum of 1+ million clusters on a disk)
to 64K blocks, but there are some other bits that were defined with the
change (such as for INIT /LIMIT or INIT /SIZE).

Best thing to do is if you want to access disks from older versions is to
initialize the disks on those older versions, but disks inited on newer
versions will work if you don't specify the newer features and the cluster
size doesn't create an oversized bitmap.