CPFMTXA/ICKDSF will put a VTOC on the system that shows no space
available. I know of nothing that also shows all space allocated. Both
are needed to prevent allocation and insure that the VSE Bit can never
cause a problem.
Regards,
Richard Schuh
________________________________
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On Behalf Of Scott Rohling
Sent: Monday, September 29, 2008 11:20 AM
To: [email protected]
Subject: Re: CPFMTXA VOLUME FORMATTING QUESTION
A colleague here supposedly wrote something that puts a 1 track
DSCB on cylinder 0 that shows it with no free space to MVS.. but no one
can find it :-) I've been hunting around for such a thing because the
backups of the VM volumes that are supposed to take place on MVS are
getting skipped... (the details are sketchy but it's related to having a
valid VTOC and space being used)
Does anybody have some code they can share that does such a
thing (make the volume visible to z/OS with a valid VTOC and show the
volume as being used?)
Thanks !
Scott Rohling
On Mon, Sep 29, 2008 at 11:46 AM, Schuh, Richard
<[EMAIL PROTECTED]> wrote:
Only if the volume label points to somewhere that used
to be a VTOC that
has not been overwritten.
Unless things have changed in the last few years, the
VTOC written when
formatting the disk as a CPVOL does not go far enough.
If the MVS DASD
Storage Allocation Routine is interrupted while the
checking for free
space on the volume, a bit (formerly known as the DADSM
Interruption Bit
or DOS VTOC bit, currently known as the VSE bit, name
DS4DOSBT in the F4
DSCB DSECT) is left on. The next time MVS attempts to
allocate space on
the volume, it will try to create proper free space
records. It does
this buy starting with an F5 DSCB that shows all space
available on the
disk. It then runs the F1 and F3 chains, allocating each
described
extent. Since there are no allocated extents on a CPVOL
formatted disk,
it shows the entire volume as being available for space
allocation.
There needs to be at least 1 F1 DSCB allocating the
entire volume to a
space-holder dataset to prevent this highly unlikely
occurrence.
Regards,
Richard Schuh
> -----Original Message-----
> From: The IBM z/VM Operating System
> [mailto:[EMAIL PROTECTED] On Behalf Of Mike
Walter
> Sent: Monday, September 29, 2008 9:18 AM
> To: [email protected]
> Subject: Re: CPFMTXA VOLUME FORMATTING QUESTION
>
> What about the dummy VTOC that CPFMTXA (or ICKDSF's
CPVOL
> command) places on cylinder zero?
> Without that dummy VTOC, which makes it appear to
Other
> Systems that there is no space left on the DASD, they
can and
> **WILL* write on it!
