[Info-vax] Sizing up Disks with Shadowing

[John Santos]

In article <daab800d-0795-4749-8ee8-069d97844072
@x6g2000prc.googlegroups.com>, ken.fairfield at gmail.com says...> 
> On Aug 11, 2:24 pm, Ken Fairfield <ken.fairfi... at gmail.com> wrote:
> [...]
> > In another follow-up, you write:
> >
> > > These disks were probably initialize way back on an earlier version of
> > > VMS.  I wonder if that will make a difference?
> >
> > I don't know, but I don't think so.  I think the
> > SET VOLUME/LIMIT does all the reorganization
> > that's needed.  (Does anyone know if it recreates
> > BITMAP.SYS or some such?)
> 
> Sorry, on reflection I *think* the expansion limit
> *is* dependent on the size of BITMAP.SYS, which
> is created when the disk is initialized.  I'd be happy
> to be corrected, but I suspect that's the hard limit.
> 
> In which case, yes, disks initialized a long time
> ago would be limited by the smaller size of the
> older BITMAP.SYS.  If that's the case, I'd go
> with a BACKUP/IMAGE/NOINIT from the
> current system disk to your big disk, etc.
> 
>    -Ken

Yes, which is why the stuff you said earlier about a /LIMIT
being absolutely required in order to use dynamic volume
expansion is not quite correct!  ;-)

The actual limit for volume expansion is the number of bits
in BITMAP.SYS times the clustersize of the disk.  With a
big clustersize, there are more "spare" bits in BITMAP.SYS
(since its minimum size is one cluster), and so you might
have enough extra bits at the end of it to map the additional
clusters on the larger disk.  If this is the case, you can
expand the disk to new size without doing a SET VOLUME/LIMIT.

Buried in the output of $ SHOW DEVICE/FULL is the current
expansion size limit (at least on VMS V8.3.)

If the expansion size limit is much larger than expected
on your system disk, maybe you increased it while upgrading
VMS?  I think the upgrade procedure gives the option of
converting the system disk to ODS-5 (on Alpha and Itaniums,
anyway), and I think at the same time, you might be able to
up the expansion limit.  New system disks might be initialized
with a bigger limit.  In any case, while booted from the CD
during an upgrade, it only takes a minute to go to command
mode ($$$ prompt), mount the system disk, set volume/limit
on it, dismount, and proceed with the upgrade.

-- 
John Santos
Evans Griffiths & Hart, Inc.