Browse Prior Art Database

Guest Identifier in EMIF for VM Guests in Sysplex

IP.com Disclosure Number: IPCOM000115293D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 157K

Publishing Venue

IBM

Related People

Brice, FW: AUTHOR [+3]

Abstract

Disclosed is the concept of a Guest Identifier (GID) for use in a Virtual Machine (VM) environment with a variation of IBM* Enterprise Systems Connection* (ESCON) Multiple-Image Facility (EMIF). The GID is an identifier that can be assigned by the VM control program to a guest operating system running in a virtual machine. The GID is in contrast to the EMIF Image Identification code (IID) that is bound to a specific Central-Processing-Complex (CPC) image in EMIF. The GID increases the usefulness and flexibility of VM support for guests participating in sysplexes.

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Guest Identifier in EMIF for VM Guests in Sysplex

      Disclosed is the concept of a Guest Identifier (GID) for use in
a Virtual Machine (VM) environment with a variation of IBM*
Enterprise Systems Connection* (ESCON) Multiple-Image Facility
(EMIF).  The GID is an identifier that can be assigned by the VM
control program to a guest operating system running in a virtual
machine.  The GID is in contrast to the EMIF Image Identification
code (IID) that is bound to a specific Central-Processing-Complex
(CPC) image in EMIF.  The GID increases the usefulness and
flexibility of VM support for guests participating in sysplexes.

      One area addressed by the GID is the fencing function within a
sysplex.  The fencing function allows the isolation of an individual
operating system through the fencing of a CPC-image from the rest of
the sysplex, based on the IID received in the fencing command.  The
fencing is performed within the channel subsystem of a CPC that
receives a command from another CPC within the sysplex.

      Such fencing-by-IID is unsatisfactory in a VM environment.
Preferred guests (i.e., high-performance guests) are each assigned a
unique IID by virtue of the fact that they achieve their high
performance through the dedicated use of a CPC-image within EMIF.
However, such guests use subchannel-images not only in their assigned
CPC-images, but also in the CPC-image assigned to the VM control
program.  Preferred guests use subchannel-images in the control
program's own CPC-image (1) when a subchannel dedicated to a guest is
not defined as a shared subchannel within the CPC's configuration
definition; and (2) when multiple guests share the same
subchannel-image concurrently (i.e., for VM minidisks).

      Hence for proper fencing support in a VM EMIF environment, the
I/O operations of each guest participating in a sysplex must be
identified as to the actual guest, not just the CPC-image, issuing
the I/O request.  Fencing of a particular guest must apply to all
subchannels used by the guest, not just those within a given
CPC-image.

      Another area addressed by the GID is that of allowing VM's
non-preferred guests (i.e., pageable guests, to which CPC-images
would not be dedicated) to participate as sysplex members, as
available message subchannel-images permit.  Specifically, it is
desirable that a non-preferred guest be able to use message devices
(albeit without the performance benefits of interpretive execution)
that are associated with a CPC-image when a preferred guest assigned
to that CPC-image is not a member of a sysplex and hence is not using
the message devices in the CPC-image.

      The GID addresses these areas by providing more flexibility and
dynamicism than the IID.  The IID essentially represents specific
channel-subsystem resources (in particular, the subchannel-images
associated with a given CPC-image), and the IID values associated
with these resources are fixed regardless of the...