HP Archive Backup System for OpenVMS Guide to Operations

Comment:
E.4 Multipathing
ABS/MDMS Support for Fibre Channel
E.4 Multipathing
• Other than the unique naming convention for FC devices, the application (such as listed
above) does not see the FC connected storage resource as being any different than a similar
direct connected SCSI device. The FC as seen from a high level application is merely a
communication channel, whose protocol is provided by the device driver and host bus
adapter, or the Modular Data Router.
• MDMS V3.2 and above only controls the access to the share tape storage for the ABS,
HSM, and SSM if the operator makes use of MDMS to allocate the tape drive. Further
• MDMS must be running on at least one node of each cluster or standalone system that
shares the tape library. All this within the same MDMS Domain only.
• The tape drives must be set to NOSHARE.
• Any system outside of the MDMS Domain that shares the tape device is unprotected, and
can cause a conflict.
• FC environment doesn't have any universal manager who maintains the information of
devices. Since VMS does not manage the allocation of drive across two or more clusters,
MDMS polls the nodes listed in the drive object to ensure that none of the nodes listed in the
drive list has allocated the device. In case the node listed is unreachable, then MDMS
returns a drive check error. MDMS will not allow other nodes to access the drive without
knowing the status of drive on one node as it may possibly lead to a dataloss scenario.
A possible workaround is suggested bwlow:
The customer needs to create an MDMS GROUP object. The GROUP object should consist
of all the NODEs accessing the DRIVE/JUKEBOX and the DRIVE/JUKEBOX objects
should have the GROUP listed in the DRIVE/JUKEBOX objects.
At the time of system bootup the following command needs to be executed.
$ MDMS SET GROUP xyx/NODE=node_name/ADD
At the time of the system shutdown the following needs to be executed.
$ MDMS SET GROUP xyx/NODE=node_name/REMOVE
The above workaround is applicable only when the node is shutting down normally. In case
the node is not reachable when there is a network issue due to reasons other than a normal
node shutdown (E.g. Due to a node crash or due to a network cable issue) the above
workaround will not be applicable.
Another alternative the system administrator can consider is to remove the NODE name
from the DRIVE object in case of the customer wants to shutdown one of the nodes in a FC
environment.
Multipathed configurations are possible with FC as well as SCSI storage interconnect.
SMS Products support the multipathed configurations supported by Open VMS. Current version
of OpenVMS 7.3 does not support multipathing on tape devices connected to FC using MDR.
E.4.1 Configurations Tested
Multipathing is transparent to ABS and MDMS.
The following configurations have been tested on FC connected devices.
ABS/MDMS Support for Fibre Channel E–3