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Performance Considerations for OS/390 Guests
Updated 30 March 1999
When running OS/390 as a guest of VM/ESA when VM/ESA is running
in an LPAR itself,
the following functions or performance advantages are lost.
- ADMF - Asynchronous Data Mover Facility is not available to
the OS/390 guest because VM/ESA depends on PR/SM function to
make that available and the PR/SM function is already in use
by LPAR.
- DAT-on MVPG used by MVS or OS/390 is lost for the guest
when VM/ESA is run on an LPAR. Note, that DAT-off MVPG such
as that used by DB2 for VM and VSE is available, except on
some older machines.
- I/O Assist and the ability to run multiple preferred
guests is lost in VM/ESA when running in an LPAR. Only a
single V=R guest without benefit of I/O Assist is permitted
when VM/ESA is running in an LPAR.
There are other features that are unavailable to MVS and OS/390 when
running as a guest of VM/ESA, regardless of whether VM itself is running
in basic mode or in an LPAR. Storage reconfiguration is one such
function.
An MVS or OS/390 guest cannot use dynamic-I/O configuration to
reconfigure the real I/O hardware. However, the guest's virtual-I/O
configuration can be dynamically changed. The MVS or OS/390 HCD
component can be used in the normal manner to change the software view
of the MVS or OS/390 I/O configuration. VM's dynamic-I/O-configuration
support can be used to perform any necessary hardware I/O configuration.
VM operator commands and directory facilities can be used to assign or
remove I/O resources to or from a guest's virtual-machine configuration.
The VM/ESA guest coupling support is available to OS/390 guests
even when VM/ESA is running in a logical partition.
The following links may have some additional information of
interest.
Thanks to Damian Osisek and Frank Brice for the bulk of this
material.
Bill Bitner owns any errors.
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