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IBM Tivoli Storage Manager for Space Management for UNIX: User's Guide


Summary of the HSM Client

The IBM Tivoli Storage Manager for Space Management for UNIX (HSM) client migrates files from your local file system to storage and recalls them either automatically or selectively. Migrating files to a distributed storage device frees space for new data on your local file system, and takes advantage of lower-cost storage resources that are available in your network environment.

Your Tivoli Storage Manager administrator defines management classes to files. You, as root user:

These options and settings determine which files are eligible for automatic migration, the order in which files are migrated, where the migrated files are stored, and how much free space is maintained on your local file system. You prioritize files for migration by their file size, or by the number of days since your files were last accessed. Stub files that contain the necessary information to recall your migrated files remain on your local file system so that the files appear to reside locally. When you access migrated files, they are recalled automatically to your local file system. Contrast this with archiving, which completely removes files from your local file system.

The HSM client provides space management services for locally-mounted file systems, and it migrates regular files only. It does not migrate character special files, block special files, named pipe files, or directories.

File migration, unlike file backup, does not protect against accidental file deletion, file corruption, or disk failure. Continue to back up your files whether they reside on your local file system or in storage. You can use the IBM Tivoli Storage Manager backup-archive client to back up and restore migrated files in the same manner as you would back up and restore files that reside on your local file system. If you accidentally delete stub files from your local file system, or if you lose your local file system, you can restore the stub files.

For planned processes, such as storing a large group of files in storage and returning them to your local file system for processing, use the archive and retrieve processes. You can use the backup-archive client to archive and retrieve copies of migrated files in the same manner as you would archive and retrieve copies of files that reside on your local file system.


Migrating Files from Your Local File System

Once file migration begins, the HSM client sends a copy of your file to a server and replaces the original file with a stub file on your local file system. The file appears as though it resides on your local file system. A stub file is a small file that contains required information to locate and recall a migrated file, and to respond to specific UNIX commands without recalling the file. The server places your migrated files in storage volumes on disk devices, or devices that support removable media, such as tape. Your Tivoli Storage Manager administrator defines and groups the storage volumes into storage pools.

The HSM client provides both automatic and selective migration. Automatic migration monitors space usage and automatically migrates eligible files according to the options and settings that you select. The HSM client provides two types of automatic migration: threshold migration and demand migration.

Threshold migration maintains a specific level of free space on your local file system. When space usage reaches the high threshold that you set for your file system, eligible files are migrated to storage automatically. When space usage drops to the low threshold that you set for your file system, file migration stops.

Demand migration responds to an out-of-space condition on your local file system. Demand migration starts automatically if your file system runs out of space. As files are migrated, space becomes available on your file system and the process that caused the out-of-space condition continues.

Selective migration moves specific files from your local file system to storage. For example, if you know that you will not be using a particular group of files for an extended time, you can migrate them to storage to free additional space on your local file system.


Premigrating Files from Your Local File System

For faster migration, use the premigration process to prepare your files for automatic migration. Files are copied to storage while the original files remain on your local file system. The next time you need free space on your local file system, the HSM client quickly changes premigrated files to migrated files without requiring additional time to copy them to storage. The HSM client verifies that files have not changed since they were premigrated. Copies of the files are replaced with stub files on your local file system.

Files are premigrated each time automatic migration completes if:


Recalling Your Migrated Files

You can recall a migrated file to your local file system from storage using either transparent recall or selective recall.

Transparent recall automatically returns a migrated file to your local file system when you access the file. If you change the recall mode for a migrated file, or for a specific execution of a command (AIX JFS only), you change how the HSM client recalls a migrated file.

Note: The following recall modes apply only to read operations. For write and truncate operations on migrated files, always the normal recall mode will be used.

Migrate-on-close

(Valid for AIX JFS file systems only)

Temporarily recalls a migrated file to its originating file system. The recalled file remains on your local file system only for as long as it is open. When you close the unmodified file, a stub file replaces it on your local file system. The file is migrated again. It is not necessary to send a copy of the file to storage because you did not modify the file. The copy that currently resides in storage remains valid.

Normal
Recalls a migrated file to its originating file system. The recalled file remains on your local file system. When you close the unmodified file, the copy that currently resides in storage remains valid. The local copy is premigrated.

Read-without-recall

(Valid for AIX JFS 4.3 file systems only)

Reads a migrated file from storage without storing it on your local file system. The HSM client reads information sequentially from the migrated file, and caches information that it reads from the file into a memory buffer on your workstation. The read-without-recall mode is intended for single-access, sequential reads of non-executable files. |

|Partial file recall

|(Valid for AIX GPFS HSM only)

|Recalls a portion of a migrated file. This avoids having to recall |an entire, potentially large file, when only a small portion of the file is |required by an application. When HSM intercepts a read request for a |file configured for partial file recall, it will calculate which portion of |the file to recall based on the offsets contained in the read request. |This results in time and disk space savings, since only a portion of the file |is recalled, using less local disk space. See Recall Your Files in an AIX GPFS Environment for more information. |

|Streaming recall mode

|(Valid for AIX GPFS, Linux GPFS, and Solaris VxFS)

|Streaming recall mode enables or disables an asynchroneous recall of |migrated files. The recalled portion of the file can be accessed while |the file is recalled. Streaming recall mode is valid for read-only |operations on the file.

|Note: Partial file recall mode takes precedence over |streaming recall mode.

|See Streaming Recall Mode for more information.

Selective recall returns specific, migrated files to your local file system. You select the files that you want to recall. When you selectively recall a file, you store it in its originating file system. Selective recall overrides the recall mode that you set for a migrated file with normal recall mode.


Reconciling Your File Systems

You, as root user, set reconciliation to automatically reconcile file systems at intervals. The default interval is every 24 hours. Set the value for reconcileinterval larger than zero. For a larger number of file systems, increase this value to reduce the impact that the dsmreconcile command might have on system performance. This reconciles your local file system with the server that you contact for space management services. When you reconcile your file system, you also update other space management-related information.

When you modify the data of a migrated or premigrated file, or erase a migrated or premigrated file from your local file system, you retain an obsolete copy of the file in storage. During reconciliation, any obsolete copies of migrated or premigrated files are marked for expiration. The copies expire and are removed from the server after the elapsed expiration date.


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