OpenVMS Cluster Systems - OpenVMS Systems - HP

Figure 6–3 Configuration with Cluster-Accessible Devices
Local
Devices
MSCP
Served
MSCP
Served
VAX Local Disk Alpha
CI
SCSI
SCSI
Quorum Disk
Star Coupler
CI
HSJ HSJ
Cluster Storage Devices
6.1 Data File Sharing
MSCP
Served
MSCP
Served
Local
Devices
ZK−1637−GE
By design, HSC and HSJ disks and tapes are directly accessible by all OpenVMS
Cluster nodes that are connected to the same star coupler. Therefore, if the
devices are dual ported, they are automatically dual pathed. Computers
connected by CI can access a dual-ported HSC or HSJ device by way of a
path through either subsystem connected to the device. If one subsystem fails,
access fails over to the other subsystem.
Note: To control the path that is taken during failover, you can specify a
preferred path to force access to disks over a specific path. Section 6.1.3 describes
the preferred-path capability.
6.1.3 Specifying a Preferred Path
The operating system supports specifying a preferred path for DSA disks,
including RA series disks and disks that are accessed through the MSCP server.
(This function is not available for tapes.) If a preferred path is specified for a
disk, the MSCP disk class drivers use that path:
• For the first attempt to locate the disk and bring it on line with a DCL
command MOUNT
• For failover of an already mounted disk
In addition, you can initiate failover of a mounted disk to force the disk to the
preferred path or to use load-balancing information for disks accessed by MSCP
servers.
You can specify the preferred path by using the SET PREFERRED_PATH DCL
command or by using the $QIO function (IO$_SETPRFPATH), with the P1
parameter containing the address of a counted ASCII string (.ASCIC). This string
Cluster Storage Devices 6–5