Truncation Overview

Truncation operations fall into two categories. The first category is the truncation that is performed as part of the normal StorNext processing. The second category is the “space management” truncation policies that are run only when the disk usage reaches certain key points.

For each file system defined on the MDC, there must be an entry in the /usr/adic/TSM/config/filesystems file.

There are five variables specified for each file system:

  1. Low-water mark (default value is 75%)
  2. High-water mark (default value is 85%)
  3. Min-Use mark (default value is 75%)
  4. Min-Use enable (default is true)
  5. Truncation enable (default is true)

If truncation is not enabled on a file system, no files residing within that file system will ever be truncated. If truncation is enabled on a file system, as files are stored to media they automatically become truncation candidates unless they are marked for immediate truncation.

Thus, a file can be truncated during one these operations:

  1. Immediately after store (only if policy class is configured)
  2. Daily truncation
  3. LoSpace truncation
  4. Emergency relocation

These truncations are performed as part of the normal processing done by StorNext.

This refers to truncation performed immediately after all copies of a file are stored to media. This is enabled on a policy class basis and can be enabled with this command:

fsmodclass <classname> -f i

The default is that a stored file becomes a truncation candidate. The file will be dealt with through normal truncation processing. Immediate Truncation can also be enabled on a file-by-file basis by using the fschfiat command:

fschfiat -t i <filename>

The fs_tierman TSM daemon kicks off policy-based truncations each day after midnight. In this case the call is:

fspolicy -t -c <class> -m <class-trunc-min-time> -z 1

This processes each defined policy class within StorNext until all policy classes have been completed. After the fspolicy has been run against all policy classes, the daemon waits until the next day to run them again.

Each of these class-based truncation policies truncates eligible candidates until either the min-use mark, if enabled, or the low-water mark is reached or it runs out of truncation candidates. At that time it terminates execution.

An eligible truncation candidate is a file that has not been accessed during the truncation mintime interval.