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Tivoli Space Manager for UNIX Using the Hierarchical Storage Management Clients

Select Space Management Settings

When you add space management to your file systems, select space management settings that will control the following:

This information is stored in the dsmmigfstab file located in config/dsmmigfstab. Table 11 displays a sample dsmmigfstab file.

Table 11. Sample dsmmigfstab File

FS Name High (%) Thrshld Low (%) Thrshld Premig (%) Percent Age Factor Size Factor Quota Max
Candidates
Stub
Size
Server Name
/home 90 80 - 1 1 200 100 4095 Lincoln
/migfs1 80 60 40 0 1 100 200 8191 Lincoln
/migfs2 95 75 - 1 0 100 100 2047 Lincoln

At any time after you add space management to your local file systems, you can update the settings, if necessary.

Copy several files into your migrated file system after you add space management and run the dsmmigrate command. If you are running open registration, the command prompts you for your node password and contact information the first time that you run it.

The following sections provide information to help you select space management settings for your file systems.

Minimum File Size for Migration

The HSM client does not migrate a file unless doing so saves space on your local file system. For AIX JFS file systems, before a file is considered for migration, the size must be greater than both the stub file size plus one byte and the file system fragment size. If the minmigfilesize option is defined, the file must be greater than this option value. For example, if the stub file size is 2047 bytes, and the defined block size for a file system is 4096 bytes, the file size must be greater than 4096 bytes before it is eligible for migration.

For AIX GPFS and Solaris VxFS file systems, the file size must be greater than both the stub file size and the file system block size before it is eligible for migration.

Set the High and Low Threshold Percentages

The threshold percentages that you set for your file system affect when threshold migration starts and stops. A high threshold determines when threshold migration starts. A low threshold determines when file migration stops.

Specify a value of zero through 100 percent. The default for a high threshold is 90 percent. The default for a low threshold is 80 percent. For example, if you allocate 10 GB for a file system, and you must maintain at least 1 GB of free space, set the high threshold to 90 percent. If space usage equals or exceeds 90 percent when the HSM client checks space usage on your file system, files automatically begin migrating to TSM storage. The HSM client migrates files beginning with the first file that is listed in the current migration candidates list for your file system.

The percentage that you specify for a low threshold must be the same as, or lower than, the percentage that you specify for a high threshold. For example, to stop migrating files when there are 20 MB of available free space on your file system, set the low threshold to 80 percent.

Note:
If the high threshold and the low threshold are the same, space usage must exceed the low threshold before threshold migration begins.

If there are no additional candidates in the migration candidates list after threshold migration starts, and if space usage drops below the high threshold that you set, threshold migration stops. The dsmscout daemon builds a new migration candidates list when candidates are available on your file system. Threshold migration starts again the next time your file system exceeds the high threshold.

Set the Premigration Percentage

The premigration percentage controls premigration of additional files after threshold or demand migration completes. The names of any migrated files are removed from the current migration candidates list. To premigrate the next files that are listed in the migration candidates list, copies of the files are sent to TSM storage, and the original files remain as premigrated files on your local file system.

The default for the premigration percentage is the difference between the percentage that you specify for the low threshold and the percentage that you specify for the high threshold. The default percentage premigrates enough files to make the next occurrence of threshold migration faster. For example, if the high threshold is 90 percent and the low threshold is 80 percent, the premigration percentage is 10 percent. When space usage drops to 80 percent, additional files premigrate until at least 10 percent of the occupied space on your file system contains premigrated files that are listed at the beginning of the current migration candidates list. The next time threshold migration is required, the HSM client replaces those files with stub files on your local file system. This quickly reduces space usage to a low threshold without requiring additional time to copy the files to TSM storage.

If demand migration is required, having your eligible files already premigrated hastens that process as well. The HSM client quickly releases at least ten percent of the space on your local file system, and migrates any additional files that are necessary to return space usage to the low threshold.

During premigration, the HSM client skips any files that are premigrated and premigrates only those files that are required to reach the premigration percentage. Increase or decrease the premigration percentage when you want to change that percentage.

If the percentage that you specify for the low threshold is the same as the percentage for the high threshold, the default premigration percentage is zero. The HSM client does not premigrate any files after threshold or demand migration completes.

If the premigration percentage equals or exceeds the percentage that you specify for the low threshold, the HSM client premigrates all remaining files in your file system that are currently eligible for automatic migration.

Set the Age and Size Factors

Set the age and size factors to determine the order in which eligible files migrate to TSM storage during automatic migration. The age factor determines how much consideration is given to the number of days since a file was last accessed. The size factor determines how much consideration is given to the size of the file. Files are prioritized for automatic migration in descending order by their priority score. Set a value from zero through 999999999 for both age and size factors. The default is one for both factors.

Table 12 displays how to prioritize your files for migration. If a resident file and a premigrated file have the same priority score, the HSM client assigns the premigrated file a higher priority.

Table 12. Setting the Age and Size Factors

Prioritize Your Files Set the Factors
Prioritize your files for migration by age only. Set the age factor to one and the size factor to zero.
Prioritize your files for migration by size only. Set the age factor to zero and the size factor to one.
Prioritize your files for migration according to their age. Increase the age factor.
Prioritize your files for migration according to their size. Increase the size factor.
Prioritize your files for migration in order by age, and within age, by size. Set the size factor to one, and set the age factor to the size of the largest file that you want to store, or to the size (in 1 KB blocks) of the file system itself. The HSM client assigns the highest priority to the oldest files. If two or more files are the same age, files are prioritized by size.
Prioritize your files for migration in order by size, and within size, by age. Set the age factor to one, and set the size factor to the number of days equal to the longest life span of a file on your file system. The HSM client assigns the highest priority to the largest files. If two or more files are the same size, files are prioritized by age.

Set the Quota

The quota that you set determines the maximum number of megabytes of data that you can migrate and premigrate from your file system to storage. Specify a quota value from zero through 999999999. The default is the number of megabytes that are assigned for your file system. For example, if 20 gigabytes are assigned for your file system, the HSM client migrates and premigrates your files from that file system until the total number of megabytes that migrate and premigrate equals 200 megabytes.

When files premigrate, they use space on both your local file system and in storage. When files migrate, stub files use some of the space on your local file system.

If you set the quota to zero for your file system, files do not migrate to storage. Set the quota for your file system to a value that is large enough to accommodate projected growth. Check with your TSM administrator to determine whether there are any restrictions on the amount of data that you can migrate and premigrate to storage.

Set the Maximum Number of Candidates

Because dsmscoutd does not perform reconcilations, this is the maximum number of migration candidates that the dsmscout daemon searches for during a scan of your file systems. When this number is reached, the dsmscout daemon stops. The range of values that you can enter are zero through 9999999. The default is 10000.

Set the Stub File Size

A stub file contains information that is necessary to locate and recall a migrated file. It can contain leading bytes of data called leader data from your original file. If you access only this data but you do not modify it, the migrated file is not recalled from TSM storage. Storing leader data in stub files is especially useful if you frequently run one or more programs that read only the information located at the beginning of a large number of files.

For HSM clients on AIX JFS file systems, the minimum stub file size is 511 bytes and the default size is 4095. You can select a stub file size that is smaller than your file system block size. However, this is an inefficient use of space on your file system. Although the HSM client uses only the number of bytes that you specify for stub files, your operating system allocates one block for each stub file. The excess number of bytes remain unused.

For HSM clients on Solaris VxFS file systems, valid stub file sizes are a multiple of the physical blocksize. For HSM clients on AIX GPFS file systems, valid stub file sizes are zero, or a multiple of the physical blocksize. The minimum physical block size is 512 bytes. The default logical block size is 4096 bytes.

When selecting a stub file size, consider the advantage of storing additional leader data (files are not recalled if only leader data is accessed and not modified), over the disadvantage of using additional space on your local file system for stub files (larger stub files consume more storage space on your local file system).


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