User's Manual

116 Migration, release, recall, and deletion
system is reached or when there are no further valid files on the release candidate list. Files not released
remain on the release candidate list.
Figure 20 Reaching the high watermark on an HSM file system
Low watermark
Low watermark is considered during a regular release triggered by reaching the high watermark on the
HSM file system. The low watermark is the parameter that defines to what percentage volume the disk
space should be freed, and stops the release when it has achieved this level. When it is reached, files that
were not released at this point remain online and are kept on the release candidate list.
Exclusion from release
In certain situations, you may prefer certain files in the HSM file system not to be released, but to remain
permanently online. The reasons for this strategy, for example, relate to the types of files you have:
• Certain files or file types of special importance demand instant access. These files must not be released.
• Certain files or file types are accessed so often that repeated releases and recalls would increase their
access times and overuse FSE resources. These files can be held permanently online, as long as their
total size is not too large.
FSE enables you to define sets of files that are excluded from the release process and kept resident on the
HSM file systems. This feature is called exclusion from release and is part of the release policy. It is defined
by the value of the ExcludeFromRelease variable in the FSE partition configuration file. Thus, the sets
of files to be excluded can be defined separately for each FSE partition.
You can also force the files that are excluded from automatic release to be put offline unconditionally. You
achieve this by releasing them manually using the fsefile --release command. Note that using this
command on the excluded files does not modify the release policy in any way. After the manually released
files are re-migrated or re-recalled, they are still excluded from automatic release.
In the FSE partition configuration template, the ExcludeFromRelease variable is commented out. Thus,
no files are excluded from release by default. You can define the files you want to keep permanently online
by uncommenting ExcludeFromRelease and specifying appropriate filenames or filename patterns.