HP Matrix Operating Environment Software - Manual (Page 67)

Understanding EVA Storage System presentation, mapping, and masking
EVA provides a presentation model for managing host access to volumes. This model allows for
explicitly defined mapping and masking, based on specific Vdisk and host initiators. This
presentation model allows a volume to be accessed by initiators on available controller host ports.
The preferred controller may be automatically configured by the EVA system or may be set to a
preferred controller by the administrator. Internally, SPM tracks hosts as collections of initiator
endpoints. When an EVA array is imported into SPM, its host port WWNs are found and equivalent
host port entries are created in SPM's catalog. During storage service provisioning automation,
presentation update requests may reference hosts that map to the EVA's host entry or new collections
of initiator endpoints.
SPM uses the hosts' initiator endpoint addresses to relate the hosts to an existing host entry on the
array if possible. The presentation update may potentially cause a unpresent operation on the
volume to clear its current presentation setting (i.e. to mask the old presentation). Then, if necessary,
host entries are created on the array.
Finally, the update results in a presentation operation to map the volume to the appropriate host.
EVA constrains host entries, disallowing a particular initiator endpoint address to exist in more
than one host entry. This means that two volumes presented to the same initiator endpoint reference
the same host entry. This means that a particular requested presentation change could affect
presentation for another volume if the request would modify the host entry. SPM looks for these
kind of side effects and blocks them.
Working with EVA Storage System host modes
With the EVA system there is a one-to-one relationship between SPM host modes and EVA host
modes.
Creating hosts on an EVA Storage System
When SPM attempts to present a volume to an initiator, it first probes the array to detect whether
this initiator is known to the array. If it is not, a new host is created for that initiator. The name
given to that host “LSM_” followed by the WWN of the initator if created by Matrix or “SPM_”
followed by the WWN of the initiator if created within SPM. SPM can show presentations that
contain hosts with multiple initiator ports, but when creating hosts, SPM always creates a host with
a single initiator port. If SPM must present a volume to an initiator that is already referenced on
the array, and if that initiator belongs to a multiple-initiator host, then all initiators for that host are
mapped to the volume. This could potentially result in a non-conformant service.
NOTE: SPM does not automatically create new folders under Host in the HP P6000 Command
View. However, if the administrator has created host entries under folders, the existing folders and
contained hosts are imported into SPM and can be referenced when specifying Fibre Channel host
requirements. Refer to HP P6000 Command View Software documentation for more information
about hosts and folders.
Backup and restore on EVA volumes
SPM supports backup and restore of HP EVA volumes by writing a management signature string
to every EVA volume managed by SPM. This string is stored in the volume's Comment field in the
array. This field should not be modified manually using HP P6000 Command View or by other
means. For more information, see
“Backup and restore” (page 17) .
Understanding EVA Storage System presentation, mapping, and masking 67