Policies and rules

This topic describes how SAN File System automates the placement of newly created files into storage pools using policies and rules.

Policies and the rules that they contain are used to automatically assign files to specific storage pools.

Policies

A policy is a set of rules that determine where specific files are placed based on the file's attributes. You can define any number of policies, but only one policy can be active at a time. If you switch from one policy to another or make changes to a policy, that action has no effect on existing files in the global namespace. The new or changed policy is effective only on newly created files in SAN File System. Moving a file does not cause the policy to be applied.

A policy can contain any number of rules. There is no limit to the size of a policy.

SAN File System performs error checking for policies in the following phases:

If your environment is set up in a non-uniform zone configuration (in which clients cannot access all volumes), you need to ensure that the rules in the active policy place files into volumes that are accessible to the clients that use them.

Tip: When SAN File System is first installed, a default policy is created and remains active until you create and activate a new one. The default policy assigns all files to the default storage pool. Although the default storage pool is created when SAN File System is first started, you must assign volumes to it before it can be used. If a user or application on a SAN File System client attempts to create new files that would be assigned to the default storage pool, and there are no volumes assigned to it, the user or application receives No Space errors.

Rules

A rule is an SQL-like statement that tells the metadata server to place the data for a file in a specific storage pool if the file meets specific criteria. A rule can apply to any file being created or only to files being created within a specific fileset or group of filesets.

Rules can specify any of these conditions, which when matched, causes that rule to be applied:
  • Fileset
  • Filename or extension
  • Date and time when the file is created
  • User ID and Group ID on UNIX® clients

SAN File System evaluates rules in order, from top to bottom, as they appear in the active policy. The first rule that matches determines the file's placement. In other words, when a client creates a file, SAN File System scans the list of rules in the active policy to determine which rule applies to the file. When a rule applies to the file, SAN File System stops processing the rules and assigns the file to the appropriate storage pool. If no rule applies, the file is assigned to the default storage pool.

Tip:
  • After a file has been created, you can check its storage-pool assignment from the administrative command-line interface using the statfile command.
  • You can use the statpolicy command from the administrative command-line interface to view the statistics about the policy rules.
  • If you base your policies on user IDs, be aware of the manner in which the UNIX tar command restores files from backup. During the restore, a file is first created from backup with the user ID of the performer of the backup and is then changed to the user ID of the original creator of the file. With SAN File System, the policy is applied to the file at creation, so the policy applies to the user ID of the performer of the backup rather than to the user ID of the original file creator.
  • During a restore or migration, a rule that uses the creation date as the placement criteria will assign a file based on the time of the restore or migration, not the original creation time, and a rule that uses a user ID or group ID as the placement criteria will assign a file based on the user ID or group ID of the restore or migration. Therefore, do not use creation time, user ID or group ID to place file.

For detailed information about creating policies and rules, see the related topics below.

Parent topic: Storage management

Related concepts
Filesets
Storage pools

Related tasks
Creating a policy
Changing the rules in a policy
Viewing policy details
Viewing policy rules

Related reference
File placement policy syntax

Terms of use | Feedback
(C) Copyright IBM Corporation 2003, 2004. All Rights Reserved.