[Info-vax] Sizing up Disks with Shadowing

[Tom Adams]

On Aug 11, 1:52 pm, Ken Fairfield <ken.fairfi... at gmail.com> wrote:
> On Aug 11, 9:53 am, Tom Adams <tadams... at yahoo.com> wrote:
> [...]
>
> > One thing I find confusing about the example:
>
> > $ initialize/shadow=(shadowmember1:,shadowmember2:)-
> > /structure=5-
> > /cluster=3/limit=3145728/erase shadowtest
>
> > That would destroy the disk contents, right?   Is that just there to
> > create the test example?   Am I suppose to issue some sort of prep
> > command for my shadowset?
>
> Not trying to speak for Bob, but yes, that is just an
> example of setting up a shadow set from scratch
> with dynamic volume expansion enabled.
>
> > I just ignore that step and:
>
> > 1. INIT the bigger disks without worrying about /limit or any other
> > qualifiers. (and do media analysis of these 7 day warranty used
> > babies.)
>
> Not exactly.  Let's review.
>
> You have an existing shadow set on a smaller physical
> disk. You're going to add a bigger disk to that small
> shadow set.  The big disk has to be initialized to be
> able to copy it into the shadow set, but all its initialization
> parameters will be overwritten by those of the existing
> shadow set.
>
> So given an existing shadow set, say, DSA1200 on $2$DKA300
> as  USERVOL, and a new member $2$DKA400, you'd do:
>
> $ initialize dka400 scratch_disk
> $ mount/system/noassist dsa1200 -
>       /shadow=$2$dka400 uservol
>
> That starts a shadow copy of DKA400 into DSA1200,
> right?
>
> HOWEVER!  You positively MUST have done
> INITIALIZE /LIMIT DKA300 as you were building
> the existing shadow set, OR you must use
> SET VOLUME /LIMIT after its been built.
> Something like,
>
> $ DISMOUNT DSA1200
> $ MOUNT/NOASSIST $2$DKA300 -
>        USERVOL /Over=Shadow
> $ SET VOLUME/LIMIT $2$DKA300
> $ DISMOUNT $2$DKA300
> $ MOUNT/SYSTEM/NOASSIST -
>    DSA1200 /SHADOW=$2$DKA300 -
>       USERVOL
> $
>
> Notice that /LIMIT needs to be used while the
> disk is NOT a member of a shadow set.  That's
> why it's best to do this at initialization time.
>
> I recommend OMITTING a value with the /LIMIT
> qualifier.  There are some (rare?) circumstances
> for which you'd want to give a value, but for the
> majority of cases, just omit it.
>
>
>
> > 1.  merge in the bigger disks
>
> Well, that's a COPY, not a MERGE...
>
> > 2.  dismount all the smaller disk
>
> > $ set volume/size=30000 disk$shadowtest
>
> Again, if you omit the value with /SIZE, the
> volume size will be set to the (physical) disk
> size of the smallest remaining (big) disk.
>
> > In which case, I never have to use the /limit qualifier.
>
> WRONG.  As shown above, you MUST use /LIMIT,
> either when you INITIALIZE the disk, OR when you
> do a SET VOLUME/LIMIT while the disk is mounted
> privately (and therefore, not a shadow member).  In
> both cases, the volume is "unavailable' when you do
> the /LIMIT.
>
> Only after /LIMIT has been done can you use the
> SET VOLUME/SIZE, and indeed, you can do that
> on a "live" mounted volume.
>
>     -Ken

These disks were probably initialize way back on an earlier version of
VMS.  I wonder if that will make a difference?