Changing the VVR Tunables
VVR provides you with a number of tunable parameters that can be tuned to a specific value, according to your requirements. For a detailed explanation of the VVR tunables, see the VERITAS Volume Replicator Planning and Tuning Guide.
The following table provides you with a quick reference to the tunables that can be modified using the vxtune utility. All tunables can be modified using the system-specific method.
| Tunable Name
|
Modifying Tunables Using the vxtune Utility
|
Auto-tuning Supported
|
|---|
vol_rvio_maxpool_sz
|
Yes
|
No
|
vol_min_lowmem_sz
|
Yes
|
Yes
|
vol_max_rdback_sz
|
Yes
|
No
|
vol_max_nmpool_sz
|
Yes
|
No
|
vol_dcm_replay_sz
|
No
|
No
|
vol_nm_hb_timeout
|
No
|
No
|
voliomem_chunk_size
|
No
|
No
|
vol_vvr_use_nat
|
No
|
No
|
volpagemod_max_memsz
|
Yes
|
No
|
Note
The volpagemod_max_memsz is a VxVM tunable that is used to specify the amount of memory, measured in kilobytes, required for caching FastResync and cache object metadata. For more information on using this tunable, refer to "Performance Tuning and Monitoring" in the VERITAS Volume Manager Administrator's Guide.
The tunables can be tuned either using the vxtune utility or by using the system-specific interface. Some of the tunables can be tuned using only the system-specific method, while the others such as the memory tunables can be tuned using both the methods. The advantage of using the vxtune utility to tune the parameters is that you do not require to reboot the system after modifying the tunable value. This is especially useful if you want to experiment with different values to arrive at an optimum value to suit your requirements. However, the changes to the tunables using the vxtune utility are non-persistent. To make the changes persistent you will still need to use the system-specific method. However, it will require you to reboot the system for the changes to take effect.
Note
The vol_min_lowmem_sz tunable is auto-tunable; depending on the incoming writes VVR increases or decreases the tunable value.
The current values for the tunables are defined in the /etc/vx/vxtunables file after you have used the vxtune utility for the first time.
Points to note when changing the value of the tunables
- When decreasing the value of the vol_rvio_maxpool_sz tunable, all the RVGs on the host must be stopped.
- When decreasing the size of the tunables vol_max_rdback_sz and vol_max_nmpool_sz, pause the RLINKs.
Changing the Tunable Values Using vxtune
You can use vxtune to display, set, or change the memory tunables that are used by VVR. The advantage of using the vxtune utility to tune the parameters is that you do not require to reboot the system after modifying the tunable value.
The vxtune utility enables you to modify the values of the following memory tunables:
vol_rvio_maxpool_sz
vol_min_lowmem_sz
vol_max_rdback_sz
vol_max_nmpool_sz
These tunable values are then updated in the /etc/vx/vxtunables file.
The vxtune utility also allows you to enable auto-tuning for the vol_min_lowmem_sz tunable. To do this, you must set this tunable to -1. However, if you do not want it to be auto-tuned then you must set it to a required value.
To display the tunables that vxtune supports
Issue the following command on the required system to display the tunables that VVR supports along with their current values and brief description:
# vxtune
The output of this command resembles:
Tunable Value Description
----------------- -------- ---------------
vol_rvio_maxpool_sz 4096 RVIO Pool Size (KBytes)
vol_min_lowmem_sz 520 Low Memory Threshold (KBytes)
vol_max_rdback_sz 4096 Readback Pool Size (KBytes)
vol_max_nmpool_sz 4096 NMCOM Pool Size (KBytes)
volpagemod_max_memsz 6144 Cache Size for FMR Metadata (KBytes)
Note that the value of the tunables is displayed in Kilobytes (KB). To display the output in bytes, use the vxtune command with the -r option as follows.
# vxtune -r
The output resembles:
Tunable Value Description
----------------- -------- ---------------
vol_rvio_maxpool_sz 4194304 RVIO Pool Size (Bytes)
vol_min_lowmem_sz 532480 Low Memory Threshold (Bytes)
vol_max_rdback_sz 4194304 Readback Pool Size (Bytes)
vol_max_nmpool_sz 4194304 NMCOM Pool Size (Bytes)
volpagemod_max_memsz 6291456 Cache Size for FMR Metadata (Bytes)
To display the values of specific tunables
Use the following command on the required host to display the value of the specific tunable:
# vxtune tunable_name
This command displays the value of the specified tunable in Kilobytes (KB).
To display the output in bytes, use the vxtune command with the -r option.
# vxtune -r tunable_name
For example, to view the value of the tunable vol_rvio_maxpool_sz, use the following command:
# vxtune vol_rvio_maxpool_sz
The output resembles:
# 65536 (KBytes)
To modify the values of the tunables
Use the following command on the required host to modify the value of the specific tunable:
# vxtune tunable_name value
The value value of the tunable can be specified in units of KB, MB, or GB. However, the value is always displayed in kilobytes (K) regardless of the units that you have specified it in. For example, if you specify a value 500MB the value will be automatically converted and will be displayed as 512000 Kilobytes. You can use the command with the -r option to display the value in Bytes.
For example, to change the default value of the vol_rvio_maxpool_sz tunable to 128MB, use the following command.
# vxtune vol_rvio_maxpool_sz 128M
To view the changed value for the tunable use the following command
# vxtune vol_rvio_maxpool_sz
 Caution
Do not edit the tunable values directly in the vxtunables file because these changes will be ignored.
Changing the VVR Tunables Using SAM
Several VVR parameters can be tuned by using the System Administration Utility (SAM). For an explanation of VVR tunables, see the VERITAS Volume Replicator Configuration Notes. To change the value of tunables persistently use the SAM utility. Note that the changes to the tunables will be effected only after the system has been rebooted.
To change the value of a tunable:
-
Type sam to bring up the SAM interface.
-
Use the Tab key to move the control to the SAM areas display.
-
Select the Kernel Configuration area to display a list of options from which you must select Configurable Parameters.
-
Scroll to the required parameter and select it. Use the Modify Configurable Parameter from the Actions option to modify the parameter as follows:
tunable_name=value;
The change will take effect only after the next system reboot.
Example 1:
To change to the modifiable tunables by using the SAM utility choose the Configurable Parameters option from Kernel Configuration.
After modifying the tunables, rebuild the kernel and reboot the system.
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