Policies and rules

This topic describes how SAN File System automates the management of files using policies and rules.

SAN File System enables you to automate the management of files using policies and rules. Properly managing your files allows you efficiently use and balance your premium and inexpensive storage. SAN File System supports these policies:

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. Manually 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 file-placement policies in the following phases:

Currently, there is no error checking for file-management policies.

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 file-placement policy is created and remains active until you create and activate a new one. The default file-placement 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 what to do with 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 identify the conditions, such as these, that when matched causes that rule to be applied:
  • Date and time when the file is created
  • Date and time when the file was last accessed
  • Fileset
  • File name or extension
  • File size
  • 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 what is to be done with that file. For example, when a client creates a file, SAN File System scans the list of rules in the active file-placement 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.

Attention:
It is recommended that you do not use creation time, user ID or group ID to place file. If you do base any file-placement rules on creation time, user IDs, or group IDs, be aware of these restore and migration considerations:
  • A rule that uses the creation date as the placement criteria assigns a file based on the time that the file was restored or migrated, not the original creation time.
  • A rule that uses a user ID or group ID as the placement criteria assigns a file based on the effective user and group IDs of the restore process, not the original file's user and group IDs.

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

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IBM TotalStorage SAN File System v2.2