MHJohnson@HI-MULTICS.ARPA (Mark Johnson) (01/24/87)
I had an `interesting' experience with volume sets that I ended up sending an SPR on that I thought others would benefit from. I started by performing an image backup of our three disk set to another set of disks in preparation of splitting our user community to the two volume sets. After doing that, the mount command failed with the duplicate volume name error message. I mounted the disks privately, used SET VOLUME/LABEL to change the volume names (seems reasonable...). Now mounting the disks I get the message `duplicate volume number already mounted'. At this point I am somewhat confused and call the support center. They recommend changing the volume set name in VOLSET.SYS. Arcane actions with COPY, ANAL/RMS/FDL, CONVERT/FDL, and my favorite editor got that changed w/ no difference. I noticed that the INDEXF.SYS file on each disk (as seen through dump) had the volume set name as part of the home block (2nd block of INDEXF.SYS). To change the file, I tried to use PATCH/ABSOLUTE/NONEW_VERSION. It does not work since the file is already open for write (by the system). I wrote a program to patch it manually (combination of direct access I/O in Pascal and use of the debugger), dismounted the disks, and found that it now complained about the bad home block! I wrote a second program that used the physical device to recompute the checksum (it is a simple word by word addition, ignoring overflow) and update it to finally get a volume set I could use. The outcome of all this mess was an SPR for the addition of a command like SET VOLUME/VOLUME_SET_NAME=xxx to change the volume set w/o this long and difficult process. Alternatively, if I had thought to use BACKUP/NOINIT/IMAGE the volume names would have been ok as well, but that requires forethought. If you are using volume sets, please be aware of this problem when you expand your system and decide to make use of the extra space by dividing your user community into the two volume sets. --Mark <MHJohnson @ HI-MULTICS.ARPA>