HP File System Extender (FSE) manual Hierarchical Storage Manager lists

Storage space allocation in an extended FSE disk buffer

In an FSE implementation where several file systems are assigned to the FSE disk buffer, the Resource Manager tries to maximize usage of these file systems. This is necessary in order to execute FSE jobs in the most efficient manner, and to speed up FSE administrative, maintenance, and backup tasks.

For all FSE job types, a round robin scheduler is used to allocate individual file systems to different FSE jobs. When an FSE job requests FSE disk buffer resources, the Resource Manager allocates the first file system which fulfills storage space requirement of the job. If no such file system is currently available, the allocation is retried after a short interval.

Since recall (efficient recall), reorganization, and maintenance (redundant copy recreation) jobs are flexible in terms of storage space requirement for FSE disk buffer, these jobs provide the Resource Manager two values: maximum and minimum amount of the required storage space. If a file system containing the maximum amount is not available, the FSE job is assigned the first file system which contains the minimum amount, and only if the latter is also not available, the allocation is delayed.

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	Gathers files that were recently accessed and changed. A dirty file can
(list of changed files)	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.

The way transitions between HSM lists and other aspects of migration, recall, release, and deletion are controlled is defined by parameters in the configuration file for the FSE partition. These parameters are described in ”Migration” on page 127, ”Release” on page 129, ”Recall” on page 136, ”Deletion” on page 137, and in ”System allocation and job priority policy” on page 142 and ”Partition allocation and job priority policy” on page 144.

HP StorageWorks File System Extender Software user guide 125