As always, I defer to Richard Corak, but note his potential gotchas as well
as agreeing that it is only safe to have the duplicates marked as being
offline at ipl.
Jim
At 02:29 PM 11/6/2005, you wrote:
At 01:00 AM 11/5/2005, you wrote:
You can't always count on the lower address volsers being found
first. That's the way it used to work before the XA/ESA I/O subsystem came
into existence. I always thought that was still the case but John
Franciscovich or one of the IBM Endicott VM gurus set the record straight a
year or two ago on this list. Now, the order of what is found first is, at
least to CP, random in that the interrupts that are returned aren't
necessarily in ascending device number sequence.
If you install this way onto duplicate volsers, you're only going to be
safe if you set the test addresses offline at ipl in SYSTEM CONFIG and then
when you bring up the test system, vary the addresses online and attach
them to the guest. That would be the thing to do until you get the volids
changed.
Jim
No. Low device address wins, as long as the low address works.
This does not mean that it is OK to have duplicate volume labels.
From my explanation, first delivered here approx March 28, 2003,
and a few times since.
`Once again, here is how CP works at initialization regarding
`volume labels.
`
`* While RDEV blocks are allocated in subchannel number order,
` they are added to the SYSRIOIX radix tree by device number.
` See HCPIIDFS.
`* Many independent tasks are started, each initializing one device.
` These tasks are started in device number order, with no
` regard for subchannel number.
` See HCPIIO near label MOUNEXT.
`* It is unpredictable when initialization for any single device
` will be completed compared to any other.
`* For DASD that are to be attached to the system, whether CPOWNed
` or user volume, an ordered list is maintained in device number
` order. If multiple RDEVs are found to contain the same volume
` label, the RDEV for the higher device number is not added to
` the list. Effectively, only RDEVs with lower device numbers
` will be attached to the SYSTEM. See HCPIISDV. Message 0954.01
` is displayed at the operator's console for duplicates at higher
` device numbers.
`
`This algorithm was changed a number of times based on customer
`feedback. If you remember some sequence that doesn't match
`this, you're probably right: at many times in the past it didn't.
`
`But remember, if the device with the lower device number is
`somehow "wrong" (doesn't respond, I/O error, whatever), all
`your planning based on these initialization rules is probably
`broken. Keep unique volume labels for everything to be
`attached to SYSTEM.
`
`Advice about OFFLINE_AT_IPL is also good to remember.
Richard Corak
Jim Bohnsack
Cornell Univ.
(607) 255-1760
