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

Mirror Copy A
Mirror Copy A'
DRAFT -- Revision 2.0
August 22, 1996Page 10
Figure 1: Typical High Availability Configuration with Standalone Mirrored Disks
data corruption. The application can run on either of the SPUs, but only one at a time.
When the primary system fails, access to the data shifts to the surviving SPU.
Also with this configuration, the loss of one of the disk drives, the cable or even one of
the host adapters in the SPU will not prevent access to the data since another copy
resides on a separate disk link. MirrorDisk/UX automatically handles the access to
multiple copies of the data in both normal and failure scenarios.
High Availability Storage Systems
A new disk storage solution, called the HP High Availability Storage System (HASS), is
available that improves the availability of JBODs. The HASS (product number A3311A
is for a deskside unit and product number A3312A[Z] is for a rack-mount unit) has the
following HA features:
optional dual, hot-pluggable power supplies
dual power cords (with dual power supplies)
dual, hot-pluggable cooling fans
up to 8 hot-pluggable 2 GB storage modules or up to 4 hot-pluggable 4 GB
storage modules
dual, internal SCSI busses (optional single internal SCSI bus)
The above high availability features make the HASS a superior choice over previous
JBOD solutions. As with any JBOD configuration, the main limitation is the maximum
number of targets possible on a given system. From a practical perspective, the HASS
is a good solution for capacities up to 400 GB mirrored (200 GB of usable storage)
when performance is the primary decision criteria. This capacity is feasible for smaller
systems only with the FC/SCSI Mux.