Tom Duerbusch wrote:
For second level VM:
2. LPAR requires dedicated packs.
Second level VM can use dedicated packs and/or minidisks from the 1st
level system.
(the only dedicated disk space you need for a second level VM system is the CP areas. All CMS minidisks can
be shared in R/O mode and you only need to replicate the CMS disks that you intend to update. Beware of
MDC when you share CMS disks in R/O mode on the second level system)
Nothing prevents one from putting CP stuff on a minidisk (just makes it
difficult to IPL it 1st level afterward though).
3. LPAR requires real hardware for communications.
Second level VM can use VCTCA, IUCV, VSWITCH for communications.
IUCV ? I didn't know CP knew how to exploit an underlying IUCV framework
! (but then, I might have missed something).
6. In the old days of LPAR, you couldn't share channels.
Dedicated 3274/3174 for each LPAR.
Two channel switches for dasd/tape.
Dedicated communication channels.
VM is much cheaper.
How about MIF/EMIF ?
7. On an IBM 370/168 1 MB of memory ran about $1 million.
VM/370 Rel 6 BSE could run in about 150 K.
Err.. Even with a small CP nucleus.. I don't think you could ever run
VM/370 R6 with less than 512K
8. Second level VM is for REAL VM SYSTEM PROGRAMMERS.
Here, I'm with you :P
For running in a LPAR:
1. It is hard to accidently shutdown your production VM system from another
LPAR.
At one time, we have all shutdown the production VM system when we thought
we were on test.
And don't you *EVER* give class A to a virtual machine running a 2nd
level VM (.. Yeah.. I've done it..shutdown.. uh oh.. did that go 1st
level ??)
2. A second level VM system may impact the first level paging subsystem.
Can't happen with LPAR.
I'll have to disagree here :P.. If your box as so much main storage, if
you run 2 partitions, you're going to indirectly affect paging because
each LPAR will have to split whatever storage is available..
3. LPAR is a simpler concept. Both VM systems are running at the same level.
You don't have to think
about which level you are issuing commands to.
But nowadays, your workstation is probably going to be running multiple
3270 sessions.. you may very well issue a command to the wrong system -
and I'm sure that's how most errors in those cases are made.
4. You get better performance of a second level system, then when running a third level system.
Depending on what you are testing, this can be important.
5. LPAR does take less VM knowledge.
.. But much more careful planning !
Just my €.02
--Ivan
