3.7.0 HP StorageWorks HP Scalable NAS File Serving Software administration guide - HP Scalable NAS 3.7 for Linux (AG513-96002, October 2009)

When a device monitor is assigned to a server, you can select the virtual hosts that
will be dependent on the device monitor. If a device monitor indicates that a device
is not functioning properly on the primary server, HP Scalable NAS transfers the
dependent virtual host addresses from the primary server to a backup server.
Event notifier services
HP Scalable NAS provides event notifier services that can be configured to respond
when certain cluster events occur. The services can send an SNMP trap to an SNMP
trap forwarding target, send email to certain addresses, or run a script. Each service
can be configured with the specific events that should trigger a response from the
service.
SNMP sub-agent
HP Scalable NAS provides an SNMP sub-agent that can be used to retrieve all
cluster-wide state and status information. For more information, see Using the HP
Scalable NAS SNMP sub-agent, page 56.
Cluster design guidelines
Be sure to consider the following guidelines when planning the physical configuration
of your cluster.
Server memory
Memory resources are consumed on each cluster server to manage the state necessary
to preserve the coherency of shared filesystems. For this reason, the servers in the
cluster should have approximately equal amounts of physical memory. As a guideline,
the ratio of memory between the smallest and largest servers should not exceed 2.
For example, the smallest server could have 1 GB of memory and the largest server
2 GB. If this ratio is exceeded (such as a 1 GB server and an 8 GB server, with a
ratio of 8), paging can increase on the smallest server to the extent that overall cluster
performance is significantly reduced.
Supported configurations
HP Scalable NAS supports up to four Fibre Channel ports per server, multiple FC
switches, and multiported SAN disks. iSCSI arrays are also supported. The following
diagrams show some sample cluster configurations using these components. In the
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