Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

462 Performance monitoring and tuning
Tuning VxVM
Tunable parameters
The following sections describe specific tunable parameters.
dmp_cache_open
If set to on, the first open of a device that is performed by an array support library (ASL) is
cached. This enhances the performance of device discovery by minimizing the overhead
caused by subsequent opens by ASLs. If set to
off, caching is not performed. The default
value is
off. The value of this tunable can only be changed by using the vxdmpadm
settune
command.
dmp_enable_restore_daemon
Set to 1 to enable the DMP path restoration thread; set to 0 to disable. The value of this
tunable can also be changed by using the
vxdmpadm command as described in
“Configuring DMP path restoration policies” on page 153.
dmp_failed_io_threshold
The time limit for retrying an I/O request or before invoking I/O throttling in DMP. The
default value is 57600 seconds (16 hours). The value of this tunable may be changed by
using the
vxdmpadm settune command. A value can also be set for paths to individual
arrays by using the
vxdmpadm command as described in “Configuring the response to I/O
failures” on page 149 and “Configuring the I/O throttling mechanism” on page 151.
dmp_health_time
DMP detects intermittently failing paths, and prevents I/O requests from being sent on
them. The value of dmp_health_time represents the time in seconds for which a path
must stay healthy. If a path’s state changes back from enabled to disabled within this time
period, DMP marks the path as intermittently failing, and does not re-enable the path for I/
O until dmp_path_age seconds elapse. The default value of dmp_health_time is
60 seconds. A value of 0 prevents DMP from detecting intermittently failing paths. The
value of this tunable may be changed by using the
vxdmpadm settune command.
dmp_log_level
The level of detail that is displayed for DMP console messages. The following level
values are defined:
1 Display all DMP log messages that existed in releases before 5.0. This is the
default setting.
2 Display level 1 messages plus messages that relate to I/O throttling, suspected
paths, repeated path failures and DMP node migration.