[Info-vax] Sizing up Disks with Shadowing

[Ken Fairfield]

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