Re: I have to use the 'O' word.

[Schuh, Richard]

And the way that a full volume is indicated was only partially correct in the good old days. I don’t know about the modern VTOCs, they may be handled much differently.   The way a volume was marked as full was to write a Format 5 DSCB indicating no free space. To complete the process, there should also have been a Format 1 DSCB describing an extent encompassing all the tracks except for the VTOC extent. There was, maybe still is, a very dangerous bit in the Format 4 DSCB that indicates either a DOS or a Damaged VTOC (DOS came first, using it for a Damaged VTOC came later. I guess in the eyes of the OS, including OS/360, VS1, SVS, and at least the early MVSes, developers, there was no difference.). Whenever the allocation routines tried to allocate space on the volume, the bit would be turned on and then turned off when allocation was finished with the volume. If this bit was on when OS tried to allocate space on the disk, the allocation routines would reconstruct the F5 DSCB chain by creating an F5 that has all space free and then sequentially read the VTOC, removing allocated extents one-by-one from this dummy F5. It would then write a chain of F5s that included all non-allocated space. For a VTOC that only had an F5 indicating no free space and no other DSCB that allocated the entire volume, the new F5 would include the entire volume except for the label track and the VTOC extent. Recovery from this was very painful, both to OS  and VM.     Regards, Richard Schuh   -----Original Message----- From: VM/ESA and z/VM Discussions [mailto:[EMAIL PROTECTED]On Behalf Of David Boyes Sent: Wednesday, February 08, 2006 7:36 AM To: VMESA-L@LISTSERV.UARK.EDU Subject: Re: I have to use the 'O' word.   They already have one (DSF CPVOL FORMAT puts an OS VTOC on VM volumes that indicates that the volume is full wrt to OS allocation).   From: VM/ESA and z/VM Discussions [mailto:[EMAIL PROTECTED] On Behalf Of Steve Gentry Sent: Wednesday, February 08, 2006 8:30 AM To: VMESA-L@LISTSERV.UARK.EDU Subject: I have to use the 'O' word. Hello. We are a VM shop only, therefore our DASD is formatted for VM and have a VM VTOC.  Is it possible to put an osvtoc  (the 'O' word <g>) on these volumes without totally reformatting the drive, etc? Thanks, Steve G.