Enabling and Disabling Cached Quick I/O for Individual Files
After using qiostat or other analysis tools to determine the appropriate files for Cached Quick I/O, you need to disable Cached Quick I/O for those individual files that do not benefit from caching using the qioadmin command.
Prerequisites
- Enable Cached Quick I/O for the file system before enabling or disabling Cached Quick I/O at the individual file level.
Usage Notes
- You can enable or disable Cached Quick I/O for individual files while the database is online.
- You should monitor files regularly using qiostat to ensure that a file's cache-hit ratio has not changed enough to reconsider enabling or disabling Cached Quick I/O for the file.
- Enabling or disabling Cached Quick I/O for an individual file is also referred to as setting the cache advisory on or off.
- See the qioadmin(1) manual page for more information.
Setting Cache Advisories for Individual Files
To disable Cached Quick I/O for an individual file
Use the qioadmin command to set the cache advisory to OFF as follows:
$ /opt/VRTS/bin/qioadmin -S filename=OFF /mount_point
Example
To disable Cached Quick I/O for the file /db01/system.dbf, set the cache advisory to OFF:
$ /opt/VRTS/bin/qioadmin -S system.dbf=OFF /db01
To enable Cached Quick I/O for an individual file
Use the qioadmin command to set the cache advisory to ON as follows:
$ /opt/VRTS/bin/qioadmin -S filename=ON /mount_point
Example
Running qiostat shows the cache hit ratio for the file /db01/system.dbf reaches a level that would benefit from caching. To enable Cached Quick I/O for the file /db01/system.dbf, set the cache advisory to ON:
$ /opt/VRTS/bin/qioadmin -S system.dbf=ON /db01
Making Individual File Settings for Cached Quick I/O Persistent
You can make the enable or disable individual file settings for Cached Quick I/O persistent across reboots and mounts by adding cache advisory entries in the /etc/vx/qioadmin file.
Cache advisories set using the qioadmin command are stored as extended attributes of the file in the inode. These settings persist across file system remounts and system reboots, but these attributes are not backed up by the usual backup methods, so they cannot be restored. Therefore, always be sure to reset cache advisories after each file restore. This is not necessary if you maintain the cache advisories for Quick I/O files in the /etc/vx/qioadmin file.
To enable or disable individual file settings for Cached Quick I/O automatically after a reboot or mount
Add cache advisory entries in the /etc/vx/qioadmin file as follows:
device=/dev/vx/dsk/diskgroup/volume
filename,OFF
filename,OFF
filename,OFF
filename,ON
Example
To make the Cached Quick I/O settings for individual files in the /db01 file system persistent, edit the /etc/vx/qioadmin file similar to the following:
#
# List of files to cache in /db01 file system
#
device=/dev/vx/dsk/PRODdg/db01
cust.dbf,OFF
system.dbf,OFF
stk.dbf,ON
Determining Individual File Settings for Cached Quick I/O Using qioadmin
You can determine whether Cached Quick I/O is enabled or disabled for individual files by displaying the file's cache advisory setting using the qioadmin command.
Note
To verify caching, always check the setting of the flag qio_cache_enable using vxtunefs, along with the individual cache advisories for each file.
To display the current cache advisory settings for a file
Use the qioadmin command with the -P option as follows:
$ /opt/VRTS/bin/qioadmin -P filename /mount_point
Example
To display the current cache advisory setting for the file cust.dbf in the /db01 file system:
$ /opt/VRTS/bin/qioadmin -P cust.dbf /db01
cust.dbf,OFF
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