Enabling Cached Quick I/O on the File System

Cached Quick I/O depends on VERITAS Quick I/O running as an underlying system enhancement in order to function correctly. Follow the procedures listed here to ensure that you have the correct setup to use Cached Quick I/O successfully.

Prerequisites

• You must have permission to change file system behavior using the vxtunefs command to enable or disable Cached Quick I/O. By default, you need superuser (root) permissions to run the vxtunefs command, but other system users do not. Superuser (root) must specifically grant database administrators permission to use this command as follows:

   # chown root:dba /sbin/fs/vxfs4.1/vxtunefs
   # chmod 4550 /sbin/fs/vxfs4.1/vxtunefs

where users belonging to the dba group are granted permission to run the vxtunefs command. We recommend this selective, more secure approach for granting access to powerful commands.

• You must enable Quick I/O on the file system. Quick I/O is enabled automatically at file system mount time.

If you have correctly enabled Quick I/O on your system, you can proceed to enable Cached Quick I/O as follows:

• Set the file system Cached Quick I/O flag, which enables Cached Quick I/O for all files in the file system.

Setting the file system Cached Quick I/O flag enables caching for all files in the file system. You must disable Cached Quick I/O on individual Quick I/O files that do not benefit from caching to avoid consuming memory unnecessarily. This final task occurs at the end of the enabling process.

Usage Notes

• Do not enable Cached Quick I/O if Oracle is using Oracle Disk Manager.

Enabling and Disabling the qio_cache_enable Flag

As superuser (root), set the qio_cache_enable flag using the vxtunefs command after you mount the file system.

  To enable the qio_cache_enable flag for a file system

Use the vxtunefs command as follows:

Example

where /db02 is a VxFS file system containing the Quick I/O files and setting the qio_cache_enable flag to "1" enables Cached Quick I/O. This command enables caching for all the Quick I/O files on this file system.

  To disable the flag on the same file system

Use the vxtunefs command as follows:

Example

where /db02 is a VxFS file system containing the Quick I/O files and setting the qio_cache_enable flag to "0" disables Cached Quick I/O. This command disables caching for all the Quick I/O files on this file system.

Making Cached Quick I/O settings persistent across reboots and mounts

You can make the Cached Quick I/O system setting persistent across reboots and mounts by adding a file system entry in the /etc/vx/tunefstab file.

  To enable a file system after rebooting

Put the file system in the /etc/vx/tunefstab file and set the flag entry:

where:

• /dev/vx/dsk is the name of a block device
• dgname is the name of the disk group
• volname is the name of the volume

Example

where /dev/vx/dsk/PRODdg/db01 is the block device on which the file system resides.

For information on how to add tuning parameters, see the tunefstab(4) manual page.

Using vxtunefs to Obtain Tuning Information

Check the setting of the qio_cache_enable flag for each file system using the vxtunefs command.

  To obtain information on only the qio_cache_enable flag setting

Use the grep command with vxtunefs:

Example

where /db01 is the name of the file system. This command displays only the qio_cache_enable setting as follows:

You can also use the vxtunefs command to obtain a more complete list of I/O characteristics and tuning statistics.

  To obtain information on all vxtunefs system parameters

Use the vxtunefs command without grep:

Example

The vxtunefs command displays output similar to the following:

For a complete description of vxtunefs parameters and the tuning instructions, refer to the vxtunefs(1) manual page.