Managing Serviceguard 12th Edition, March 2006

Understanding Serviceguard Software Components
Volume Managers for Data Storage
Chapter 3 121
Cluster Startup Time with CVM
With CVM, all shared disk groups (DGs) are imported when the system
multi-node’s control script starts up CVM. Depending on the number of
DGs, the number of nodes and the configuration of these (number of
disks, volumes, etc.) this can take some time (current timeout value for
this package is 3 minutes but for larger configurations this may have to
be increased). Any failover package that uses a CVM DG will not start
until the system multi-node package is up. Note that this delay does not
affect package failover time; it is a one-time overhead cost at cluster
startup.
Propagation of Disk Groups with CVM
With CVM, disk groups are created on one cluster node known as the
CVM master node. The cluster has to be running to create shared disk
groups. CVM will validate that each node can see each disk and will not
allow invalid DGs to be created.
Redundant Heartbeat Subnet Required
Serviceguard recommends that you configure all subnets that
interconnect cluster nodes as heartbeat networks, since this increases
protection against multiple faults at no additional cost.
Heartbeat configurations are configured differently for CVM 3.5 and 4.1.
Redundancy of the networks can be done in one of the following ways:
1) dual (multiple) heartbeat networks
2) single heartbeat network w/standby lan card(s)
3) single heartbeat network w/APA
CVM 3.5 only supports options 2 and 3. With CVM 4.1, options 1 and 2
are the minimum recommended configurations.
Comparison of Volume Managers
The following table summarizes some of the advantages and
disadvantages of the volume managers that are currently available.