User's Manual

110 Migration, release, recall, and deletion
simpler process that does not require an FSE job. It is managed and executed locally by the Hierarchical
Storage Manager (HSM).
FSE disk buffer
Files that are either waiting for migration and are not yet written to the FSE media, or have been recalled
and are not yet recreated on the HSM file system, are copied to the FSE disk buffer. The disk buffer holds
temporary files that are waiting for resources and allows FSE to unlock files on the HSM file system during
migration, and de-allocate FSE media during recall as fast as possible. Usually, a separate disk partition is
allocated for the FSE disk buffer to improve robustness and to avoid potential data loss.
Temporary FSE disk buffer files are located in a special directory. They are managed by the Back End
Agent. The disk buffer directory is platform-dependent.
Linux specific
FSE disk buffer files are located in the directory /var/opt/fse/diskbuf.
Windows specific
FSE disk buffer files are located in the directory %InstallPath%\var\diskbuf.
The value of %InstallPath% depends on the choice made in the FSE installation process. It defaults to
C:\Program Files\Hewlett-Packard\FSE.
The following figure shows how the disk buffer is used.
Figure 17 Migration and recall path
Hierarchical Storage Manager lists
All migration and release jobs are carried out using Hierarchical Storage Manager (HSM) lists. These lists
provide information about the candidates to be migrated or released and gather them accordingly. FSE
executes migration or release once for a group of files rather than executing these jobs separately for each
file thus improving performance. However, recall is executed for each file separately in order to fulfill the
user’s request for a specific offline file without delay.
HSM maintains three types of lists: a list of changed files—a so-called “dirty files” list—a migration
candidate list, and a release candidate list. Each file entry can only appear on one list at a time. Either it
is a dirty file, and should not be migrated yet, or it is a migration candidate and is waiting for migration,
or it is a release candidate and is waiting to be released. Once a file is released, it is cleared from the
release candidate list. The file is then offline until the next recall. Offline files are not a part of any list. Their
status is recorded in the HSM file system in the HSM attributes (in the native file system’s extended
attributes).
Table 2 Types of HSM lists
FSE HSM list Description
Dirty file list
(list of changed files)
Gathers files that were recently accessed and changed. A dirty file can
be either a new file or a file that has changed since the last migration or
recall. A file is added to this list once you start changing it.
Migration candidate list Once a changed file is not modified for a certain period of time, the file
is moved onto the migration candidate list.
Release candidate list Gathers online files that have already been migrated and have not
changed since then, and files that were brought online by recall.