The Question is:
We have an Alphaserver 2100 cluster that uses DSSI disks in storageworks
boxes and HD05 controllers. This still works but is very old and we need a
significant increase in disk capacity. The old system uses OpenVMS
shadowing for redundancy.
We bought a BA356 storageworks box full of large ultra-SCSI disks and two
KZPAC-AA raid controllers with appropriate cables and personality module.
The raid system works perfectly, but cannot be used in a cluster, that is,
disks connected to both Alphase
rvers at the same time.
As a fallback, can we use KZPBA-CA non-raid controllers and OpenVMS raid
software as a SCSI cluster disk system?
The OpenVMS version is V7.1-2, but we are willing to upgrade anything as
The Answer is :
The OpenVMS Wizard will here assume that the disk hardware redundency
provided by volume shadowing (also refered to as disk mirroring) is
the core reason for the particular application of RAID, and not disk
striping nor larger volume capacity requirements that can also be
achieved with various RAID configurations.
As a general rule, the SCSI buses emanating from backplane-based RAID
controllers (eg: KZPAC RAIDarray 230) are not supported for multihost
SCSI operations on OpenVMS. (Host-based volume shadowing can be used
across these backplane-based RAID controllers, but that may or may not
be a desirable storage configuration in your particular environment.)
As a general rule, host-based SCSI controllers that support SCSI TCQ
(Tagged Command Queuing) generally are supported for multihost SCSI
configurations. Additional configuration requirements:
o one or more cluster communications interconnects (eg: FDDI,
Gigabit Ethernet, CI, etc) are a requirement for any multihost
SCSI configuration, as the OpenVMS Cluster System Communications
Services (SCS) cannot communicate host-to-host over SCSI.
o SCSI widgets that are not transparently tolerant (re-entrant)
of SCSI bus resets (eg: magnetic tapes) are not permitted on
a multihost SCSI bus.
As a general rule, the SCSI buses emanating from various HSZ, HSJ,
and similar storage controllers can themselves be configured into
specific multihost environments -- for instance, a SCSI bus emanating
from an HSZ series controller can be connected to that of another HSZ,
with appropriate firmware revisions loaded in the controllers.
In addition to disks, HSZ-series and similar (non-backplane) disk
storage controllers are usually supported for use on multihost SCSI
buses, and -- with the appropriate OpenVMS releases, controller or
drive, and controller or drive firmware. Various disk storage
controllers can also span across host-based multihost SCSI buses,
permitting failovers to transparently occur across SCSI buses.
The KZPBA-CA series controller (PCI to wide UltraSCSI) can be used in
multihost SCSI OpenVMS Cluster configurations, though (as mentioned
earlier) one (or more) additional SCS communications interconnects
are also required. While OpenVMS Alpha V7.1-1H1 was the first release
with UltraSCSI support -- an ECO kit is available to retrofit UltraSCSI
controller support for non-multihost configurations to OpenVMS Alpha
V6.2-1H3 -- OpenVMS Alpha V7.1-2 and V7.2-1 (and later) are the OpenVMS
releases recommended as a minimum by the OpenVMS Wizard.
Also be cogniscent of and carefully follow the requirements in the
OpenVMS documentation and in the OpenVMS FAQ around the settings for
the VOTES and EXPECTED_VOTES parameters. Incorrect settings for these
system parameters can lead to cases of severe disk data corruptions.
OpenVMS Alpha V7.1 and later -- and specifically the addition of
support for SCS port allocation classes in these releases -- makes
configuring and operating a multihost SCSI environment far easier.