HP StorageWorks EVA Cluster Extension Software Administrator Guide (T3667-96045, April 2010)

0001-6e12-0000-7000-031a-0000"
---- Sample UCF.cfg end
Timing considerations
EVA Cluster Extension Software gives priority to storage system operations over cluster software
operations. If EVA Cluster Extension is invoked during a DR group member resynchronization operation
(merging) or is gathering information about the remote storage system, it waits until the requested
status information is reported. This ensures the priority of data integrity over cluster software failover
behavior.
Because the failover timing depends on the configuration of your HP SMI-S EVA server and Command
View EVA environment and the settings in the UCF.cfg file, you must evaluate the following
considerations:
• EVA Cluster Extension uses HP SMI-S to communicate with the HP EVA storage system, depending
on the settings of the SMI-S request timeout property, and the number of managed EVAs, the online
operation could time out. This can also happen if clxevarun is used in a script or called by
another program and the HP SMI-S server instance(s) cannot be reached.
• In the UCF.cfg file, if the ApplicationStartup attribute is set to RESYNCWAIT, EVA Cluster Exten-
sion tries to resynchronize disk pairs and waits until the DR group is in a normal state. Depending
on the amount of data to be transferred, it could take hours to resynchronize. If this is the case,
clxevarun may take some time to return. Do not stop clxevarun; use the SSSU command
show DR_GROUP full-path/dr-group-name or the Command View EVA or Continuous
Access EVA GUI to check the status of the DR groups.
• Depending on the amount of data that is out of sync between the source and destination vdisk
while the Continuous Access EVA replication link(s) is unavailable, a merge/resynchronization or
a full copy operation is initiated when the CA EVA replication link(s) is re-established. The amount
of delta data to be transferred between the source and destination vdisk could be large enough
for the copy process to take some time.
• To prevent the failover timeout trigger from terminating a failover command before it is finished,
the time to copy an average amount of daily processed (write) data should be measured and the
resource online timeout interval should be adjusted accordingly. Use only one (the slowest) link
used for Continuous Access EVA to measure the copy time. This ensures that the average daily
generated data can be transferred fast enough from the remote EVA storage system, even in the
event of a single surviving replication link between the EVA storage systems.
In general, because the failover environment is dispersed into two (or more) data centers, the failover
time cannot be expected to be the same as it would be in a single data center with a single shared
disk device.
Restrictions for customized implementations
The following restrictions apply when using the EVA Cluster Extension CLI:
• The EVA Cluster Extension CLI command clxevarun must be invoked before the associated disk
resources are activated.
• Associated disk resources must not be activated on any other system. If other disk resources are
activated, EVA Cluster Extension may remove write-access rights for those disk devices (putting
them in read-only mode).
CLI commands and utilities90