Components of SAM-QFS

The SAM-QFS archiving lifecycle consists of the phases described in the following sections:

• Archiving

• Releasing

• Staging

• Recycling

Archiving

The archiver automatically copies online disk cache files to archive media. The archive media can consist of either online disk files or removable media cartridges. The archiver requires that you configure the archiver.cmd file to define what to archive. You can configure the archiver to create up to four archive copies on a variety of archive media. If a file is segmented, each segment is treated as a file and is archived separately. The archiving process is initiated when files match a site-definable set of selection criteria. For more information, see Chapter 9, About Archiving.

Releasing

The releaser automatically maintains the file system's online disk cache at site-specified percentage usage thresholds by freeing disk blocks that are occupied by eligible archived files.

Releasing is the process of freeing primary (disk) storage that is used by an archived file's data. The high-water mark and low-water mark, expressed as a percentage of total disk space, are used to manage free space in the online disk cache. When online disk consumption exceeds the high-water mark, the system automatically begins to release the disk space that is occupied by eligible archived files. Disk space occupied by archived file data is released until the low-water mark is reached.

Files are selected for release depending on their size and age. If a file has been archived in segments, portions of the file can be released individually. The first portion of a file can be retained on disk for speedy access and for masking staging delays. For more information, see Chapter 14, About Releasing.

Staging

The stager restores file data to the disk cache. When a user or process requests file data that has been released from disk cache, the stager automatically copies the file data back to the online disk cache.

When a file whose data blocks have been released is accessed, the stager automatically stages the file or file segment data back to the online disk cache. The read operation immediately follows the staging operation, which enables the file to be immediately available to an application before the entire file is completely staged.

The SAM-QFS software processes stage request errors automatically. If a stage error is returned, the system attempts to find the next available archive copy of the file. Stage errors that can be automatically processed include media errors, unavailability of media, unavailability of an automated library, and others. For more information, see Chapter 15, Configuring the Stager.

Recycling

The recycler clears archive volumes of expired archive copies and makes volumes available for reuse.

As users modify files, archive copies that are associated with the old versions of these files are considered to be expired. Because these copies are no longer needed, they can be purged from the system. The recycler identifies the archive volumes with the largest proportions of expired archive copies and preserves the unexpired copies by moving them to separate volumes. The recycling process is transparent to end users.

If a removable media volume contains only expired copies, you can take one of the following actions:

• Relabel the volume for immediate reuse.

• Export the volume to offsite storage as a historical record of file changes. You can use standard UNIX utilities to restore previous versions of files from expired archive copies.

For more information, see Chapter 16, Configuring the Recycler.