I have no opinion nor real experience to add, but what about the 
Domino running in the primary with the backup servers running in a 
separate LPAR?  I offer some comments inline after each disadvantage noted.
Regards, Chuck
Neil Palmer wrote:
What is the general consensus on whether or not you need (or should)
run Domino (for email & Sametime) in a separate LPAR?  I can't really
think of a lot of advantages, just disadvantages like:
- more maintenance on the LPAR for release upgrades, PTF's, etc.
  Actually the maintenance for the primary is one good reason to have 
the servers on an LPAR.  That is, the maintenance on the primary does 
not impact the Domino Servers which can remain active on their own 
partition.  This is ideal where availability of the Domino supported 
activity is critical, even if only for its providing the interface to 
document why and for how long the primary partition is not available.
  Additionally when maintenance is done on the Domino LPAR, that could 
be limited to just HIPers and Domino Groups, to limit its downtime more 
than for a partition providing all functions.  Then additionally having 
the backup and primary Domino servers on different partitions allows the 
separation, saving from harmful changes by maintenance affecting all 
servers.  Not only does maintenance on DomSrv1 allow falling back on 
DomBck1 during the maintenance, but if the maintenance should happen to 
leave the server failed, the issues for recovery are less drastic [i.e. 
find the fix to add, versus the removal of the maintenance] and possibly 
less urgent because the backup servers are still active where the 
problem was not introduced.
- a more expensive system because of the LPAR driving requirements
for additional disk controllers and disk, driving a requirement for
an otherwise unneeded expansion unit, etc.
  The other copy of the OS can be cheaper; the i5/OS Application Server 
[Edition?].  A modified configuration can improve system performance and 
increase options for even further variations and/or refinements in the 
configuration.  An important consideration is if the Domino server(s) 
may give rise to a requirement for more disk space, such that the 
boundary for expansion may be hit sooner and with more impact, to the 
one primary partition configuration, than if planned separately from the 
beginning with a secondary partition.
- more PC server like in that you end up with unused processor and
disk resources that would be better utilized if Domino was running in
the main system/partition.
  The system is fairly efficient at sharing CPU, and configuration 
options on how to share.  Is it better to add disk [and optionally 
balance] to the one primary partition, or to each partition as required?
I can't think of any cases where errors in Domino would cause a
production system/partition to crash - but has anyone experienced
that ?
  The Subsystem gives partitioning within the main system/partition, 
and given the subsystem can end, then all should be well.  For this 
reason, indeed there is a lesser need to have a fully separate LPAR or 
physical server as one might expect with other operating systems.
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