I *think* we're discussing two related, but separate, ideas here now:
1) freezing a guest so that it is no longer active (as PHSIII suggests,
this might not be all that difficult to do.)
2) "stunning" a guest (my term, at least) where the guest is put into a
state such that "interesting" things can be done to it, e.g., move it to
a different process, make an accurate and reliable backup of it's dasd
images, etc. This appears to be (much?) more difficult to do.
As Mike Coffin points out, the guest operating systems might need to be
involved in some way....it's not enough for a Linux guest to be
"frozen", it need to be told to first dump all of it's internal i/o
buffers to dasd first (and perhaps save the sate of current TCP/IP
connections and who knows what else...). The same considerations may
apply to z/OS and VSE guests as well. CMS, on the other hand, might not
care at all.....;-)
DJ
P.S. I think Mike's idea of adding QUIESCE and RESUME commands is a
really good one. Since Linux is open source, we could do that. I expect
to see a kernel patch by Monday, Tuesday at the latest....;-)
David Kreuter wrote:
Seems to me CP already has most of this code path anyway. The free
storage limit detection will stop a machine in its tracks after the
second violation. It puts the errant machine into CP READ stopped state.
In the distant past I made some presentations on this - I'll dig
around. How deep and true this stopped state is - don't know - but
likely its a reasonable stoppage.
David Kreuter
Rob van der Heij wrote:
On 4/7/06, Phil Smith III <[EMAIL PROTECTED]> wrote:
Well, that capability isn't that hard -- V/SPOOL (now part of
CA-somethingorother-VM:Spool V/SEG-PLUS feature) has a FREEZE
capability, and ISTR it was a few lines in the right place in CP to
keep the guest from being dispatched.
I suppose you could even issue a SEND CP xxx SLEEP to stop Linux from
working, but it would cause things to time out and sessions to drop
when it takes a bit longer.
Especially with LVM, it is hard to avoid inconsistency when the backup
of the physical volumes is not done at the same time. But with LVM you
can quiesce the disk for a moment to allow the backups to be taken.
--
Rob van der Heij
Velocity Software, Inc
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