OpenVMS Cluster Systems - OpenVMS Systems - HP

Building Large OpenVMS Cluster Systems
9.5 System-Disk Throughput
IF... THEN... Comments
Few users are active
simultaneously
Most users run a single
application for extended periods
A single system disk might
support a large number of
satellites.
A single system disk might
support a large number of
satellites if significant numbers
of I/O requests can be directed to
application data disks.
For most configurations, the probability is low
that most users are active simultaneously. A
smaller and less expensive OpenVMS Cluster
system can be configured for these typical
working conditions but may suffer some
performance degradation during peak load
periods.
Because each workstation user in an OpenVMS
Cluster system has a dedicated computer, a
user who runs large compute-bound jobs on
that dedicated computer does not significantly
affect users of other computers in the OpenVMS
Cluster system. For clustered workstations, the
critical shared resource is a disk server. Thus, if
a workstation user runs an I/O-intensive job, its
effect on other workstations sharing the same
disk server might be noticeable.
• Concurrent booting activity
One of the few times when all OpenVMS Cluster computers are
simultaneously active is during a cluster reboot. All satellites are waiting to
reload the operating system, and as soon as a boot server is available, they
begin to boot in parallel. This booting activity places a significant I/O load on
the boot server, system disk, and interconnect.
Note: You can reduce overall cluster boot time by configuring multiple
system disks and by distributing system roots for computers evenly across
those disks. This technique has the advantage of increasing overall system
disk I/O capacity, but it has the disadvantage of requiring additional system
management effort. For example, installation of layered products or upgrades
of the OpenVMS operating system must be repeated once for each system
disk.
• System management
Because system management work load increases as separate system disks
are added and does so in direct proportion to the number of separate system
disks that need to be maintained, you want to minimize the number of system
disks added to provide the required level of performance.
Volume Shadowing for OpenVMS is an alternative to creating multiple system
disks. Volume shadowing increases the read I/O capacity of a single system disk
and minimizes the number of separate system disks that have to be maintained
because installations or updates need only be applied once to a volume-shadowed
system disk. For clusters with substantial system disk I/O requirements, you can
use multiple system disks, each configured as a shadow set.
Cloning the system disk is a way to manage multiple system disks. To clone the
system disk:
• Create a system disk (or shadow set) with roots for all OpenVMS Cluster
nodes.
• Use this as a master copy, and perform all software upgrades on this system
disk.
• Back up the master copy to the other disks to create the cloned system disks.
• Change the volume names so they are unique.
9–16 Building Large OpenVMS Cluster Systems