Choosing the Right Disk Technology in a High Availability Environment DRAFT Version 2.0, August 1996

DRAFT -- Revision 2.0
August 22, 1996Page 25
same LUN via both paths. The second path is for redundancy, in case of failure of the
host adapter, cable or AutoRAID controller. PVLinks does permit concurrent access to
different LUNs via both paths. To take advantage of this capability, multiple LUNs must
be defined in the AutoRAID.
The recommended number of AutoRAIDs per F/W SCSI interface changes depending
upon the I/O load and upon the number of active AutoRAID controllers. For example,
with two active AutoRAID controllers and a heavy I/O load, only four AutoRAIDs are
recommended on a given F/W SCSI interface, although seven would be theoretically
supported. This configuration also assumes that each of the two AutoRAID controllers
is connected to a different F/W SCSI host adapter. The consequence of exceeding the
recommended number of AutoRAIDs per F/W SCSI link is reduced overall performance
of the application. Performance and capacity are discussed in greater detail later.
Figure 6 shows the only supported configuration for AutoRAIDs when configured in
an HA cluster. This configuration was established for both performance and
availability reasons. There are no SPOFs in this configuration since each storage
processor is attached to a different SCSI bus and host adapter. The combination of PV
Links and controllers with AutoRAID provides very similar availability as JBODs in
association with the HA software MC/ServiceGuard and MC/LockManager.