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! >
