About Recycling

Recycling is the process of reclaiming space on archive volumes. The recycler works with the archiver to reclaim the space occupied by unused archive copies. As users modify files, the archive copies associated with the old versions can be purged from the system. The recycler identifies the volumes with the largest proportions of expired archive copies and directs the movement of unexpired copies to different volumes. If only expired copies exist on a given volume, a site-defined action is taken. For example, a volume can be relabeled for immediate reuse or exported to offsite storage, keeping a separate historical record of file changes. Users are unaware of the recycling process.

At any time, the space on an archive volume consists of the following:

• Current data, consisting of archive images that are active

• Expired data, consisting of archive images that are no longer active

• Free space, consisting of space that is not being used by active or expired archive images

The recycler keeps the amount of space consumed by expired data to the minimum defined by site-specified parameters.

The capacity of a volume is the total amount of space for data on a volume. For example, a 10-gigabyte volume with 3 gigabytes written to it has a capacity of 10 gigabytes and 7 gigabytes of free space.

New or newly labeled archive media starts with all of its capacity as free space. As data is archived to the media, the amount of free space decreases and the amount of current data increases.

As files in the file system are changed or removed, their archive images expire and the classification of their data changes from the current data to the expired data. The physical space used by the archive images does not change. However, no file in the file system points to that space. When space is recycled, these images are removed and the space they occupied become free, available for other purposes. The goal of the recycler is to transform space used by expired data into free space without losing any current data.

Recycle Process

The recycler and the archiver work together as follows:

1. The recycler marks all the current archive images that are present on a volume with the rearchive attribute.

2. If you are archiving to removable media, the recycler marks the archive volume with the recycle attribute to prevent the archiver from writing any more archive images to the volume.

3. The archiver moves all the marked images to another volume. This operation is called re-archiving. After the archiver moves the current archive images from the old volume to the new volume, the old volume contains only free space and expired space. If you are archiving to removable media cartridges, you can relabel and reuse the cartridge. If you are archiving to disk, the recycler removes the file that contains the expired archive images.

The recycler is designed to run periodically, although you can run it at any time. It performs as much work as it can each time it is invoked. The recycler has to finish marking copies for re-archiving before the archiver can re-archive the files. Sometimes expired archive images, with the rearchive attribute set, remain on media. This situation can happen under the following conditions:

• The archiver does not run after the recycler marks expired archive images.

• Media is not available for the archiver to use when moving the unexpired archive images.

• Miscellaneous archiver anomalies occur.

Between executions, the recycler keeps state information in the library catalogs and the inodes. During the recycling process, you can use the sls(1) command and its -D option to display information about a file. The output from the sls(1) command shows whether a file is scheduled for re-archiving.

Planning for Recycling

Recycling is accomplished using two methods, depending on the type of media.

Table 16-1 Media Types and Recycling Methods

For information about configuring by these methods, see Chapter 16, Configuring the Recycler.