Customizing QoSS

The following information is not essential to QoSS daily operation and management. This section describes the relationship between the fssweep and fsmove utilities to allocation policies and how files and volumes are selected for relocation.

Mapping Relocation Policies to Allocation Policies

The fssweep and fsmove utilities use relocation policies to relocate existing files. Relocation uses the file system's allocation policies to determine the current location of each file and to move files to new locations. Allocation policies also control newly created files. You can manage allocation policies using the fsapadm utility (see the fsapadm(1M) manual page). In addition, some allocation policies are automatically managed by the fssweep and fsmove utilities.

The fssweep and fsmove utilities create allocation policies that have names starting with the characters fsmove_.

Each component volume has an allocation policy with a name created by appending the volume name to the string fsmove_. For example, a volume named qoss1a has an allocation policy named fsmove_qoss1a. The file system also has an allocation policy named fsmove_ALL that includes all component volumes. VxFS default behavior is to assign fsmove_ALL to the file system's mount point as the allocation policy to be used for newly created files.

By convention, fssweep and fsmove use volume names, so you do not specify the string fsmove_ when using these utilities.

The fsmove_ALL allocation policy allows newly created files to reside on any volume. The order in which volumes are used is by ascending device index numbers. When the fssweep utility compares a newly created file's residence against a relocation policy's list of source volumes, fssweep treats the files as if they reside on the volume of lowest device index.

When you use the fssweep and fsmove utilities the first time, the file system can already contain files that have no allocation policies. The fssweep utility treats such files as though they reside in the fsmove_ALL allocation policy.

If you use the fssweep and fsmove utilities infrequently, the default allocation policy allows overflow as each volume becomes full. When this happens, it becomes ambiguous where the recently created files really reside.

You can use the fsapadm utility to create allocation policies. Avoid using names that would be created by fsmove. If a file was moved using fsapadm into an allocation policy whose name is something other than the allocation policies used by fssweep and fsmove, the fssweep utility disregards the file when it searches the file system.

You can use the fsapadm utility to create a special allocation policy named fsmove_SITE. The fssweep and fsmove utilities never create an allocation policy named fsmove_SITE. If this allocation policy exists and was established as the file system's default allocation policy, fssweep considers any file in this allocation policy as residing in any of the volumes that belong to the policy. For example, if you create fsmove_SITE to specify devices whose index numbers are 4 and 6, and if a relocation policy looks for source volume indexes of 2 and 4, files can be searched. The index 4 is common to both the relocation policy and the allocation policy. The purpose of the fsmove_SITE allocation policy is to allow allocating newly created files differently from way the fsmove_ALL allocation policy is defined, and still allow the files to be recognizable by the fssweep utility.

Relocation List Format

The relocation list is standard output from the fssweep utility that may be piped to the fsmove utility as standard input. The list consists of multiple lines of text, each of which describes one file to be moved and its destination component volume. The following is the format of the text fields:

safe_filename    destination_volumes

The safe_filename is ordinary text if the file name does not embed special characters or if it is provided on the fsmove command line. If special characters are included in the file name that fssweep provides to fsmove, the exclamation mark (!) escape character delimits the special character. The exclamation marks are followed and preceded by the two hexadecimal digits providing the internal value of the special character. This conversion allows fsmove to read special characters from fssweep correctly.

The fssweep utility provides the destination_volumes for the file to be relocated based on the policy manager's configuration policy. If there is more than one destination component volume, fsmove tries to relocate a file to each component volume, in the order specified, until the file is successfully written to one of the volumes.