Veritas Volume Manager 5.0 Release Notes HP-UX 11i v3 (5992-1952, August 2011)

• Enhancements to DMP
The following enhancements have been done to the Dynamic Multi-pathing (DMP) feature:
◦ Faster failure detection and recovery by DMP
DMP has been enhanced to allow the vxdmpadm command to be used to adjust the I/O
error recovery and I/O throttling mechanisms on individual paths.
◦ Changing DMP tunables
The values of most DMP tunables can now be set by using the vxdmpadm settune
command.
◦ Retry period for Persistent Group Reservation (PGR)
The maximum time period for which DMP retries the SCSI-3 Persistent Reserve operation
with A/P arrays can now be tuned by using the dmp_retry_timeout parameter with
the vxdmpadm command. The default value is 0 seconds. In previous releases, the default
value was set to 120 seconds, which is twice the value of the SCSI I/O timeout. However,
the default value has been set to 0 seconds, as the parameter will become obsolete in
future releases. This parameter has no direct effect on I/O processing by DMP.
Disabling a switch port can trigger a fabric reconfiguration, which can take time to
stabilize. During this period, attempting to register PGR keys through the secondary path
to an array may fail with an error condition, such as unit attention or device reset, or the
return of vendor-specific sense data. The retry period allows a fabric reconfiguration,
which is usually a transient condition, to not be seen as an error by DMP.
To display the current value of dmp_retry_timeout, type:
# vxdmpadm gettune dmp_retry_timeout
To change the value of dmp_retry_timeout, type:
# vxdmpadm settune dmp_retry_timeout=value
Do not set the value of the retry period too high. This can delay the failover process, and
result in I/O sluggishness or suppression of I/O activity during the retry period.
This parameter is not documented in the Veritas Volume Manager Administrator’s Guide
or in the vxdmpadm(1M) manual page.
• Linked break-off snapshot volumes
A new variant of the third-mirror break-off snapshot type is linked break-off snapshot volumes,
which use the vxsnap addmir command to link a specially prepared volume with the data
volume. The volume that is used for the snapshot is prepared in the same way as for full-sized
instant snapshots. However, unlike full-sized instant snapshots, this volume can be set up in a
different disk group from the data volume. This makes linked break-off snapshots especially
suitable for off-host processing applications where you may want to create the snapshot on
storage with different characteristics from that used for the data volumes.
If you change the size of volume, any snapshots that are currently linked are also resized in
the same operation.
NOTE: This feature is not available with Base-VxVM and Full VxVM bundle. To enable this
feature, you must install the FlashSnap License.
• Volume tags
Volumes can be tagged with an arbitrary tag name and optional tag value. Multiple tags can
be associated with a single volume. Such tags are used by features such as Remote Mirror,
Quality of Storage Service (QoSS), and Dynamic Storage Tiering (DST).
8 Veritas Volume Manager 5.0 Release Notes