Automatic file migration

To ensure that free space is available on your local file systems, the space management client monitors space usage and automatically migrates files whenever it is necessary. Files are prioritized for automatic migration based on the age and size settings. The dsmscoutd daemon searches these files in cycles and upon request from automatic migration.

The space management client provides two types of automatic migration: threshold and demand.

Threshold migration maintains a specific level of free space on your local file system. The space monitor daemon checks space usage on your local file systems at intervals that you specify. When space usage reaches the high threshold that you set for a file system, migration automatically sends eligible files to IBM Storage® Protect server storage. When space usage reaches the low threshold that you set for a file system, migration stops. For example, assume that you set the high threshold for your file system to 80 percent and the low threshold to 70 percent. Files begin migrating to IBM Storage Protect server storage when there is less than 20 percent of available space on your local file system. Files stop migrating when there is more than 30 percent of available space on your local file system.

More files are premigrated as specified with the pmpercentage parameter of the dsmmigfs command.

Demand migration responds to an out-of-space condition on your local file system. The space monitor daemon checks for an out-of-space condition every 10 seconds. Threshold migration starts automatically if the used capacity of your file system exceeds a certain limit. The default for this limit is 90 percent. For example, assume that you attempt to copy a large file into your file system, and there is not enough available space for the file. Eligible files begin migrating automatically from your local file system to IBM Storage Protect server storage. As space becomes available, the process continues to copy the large file to your file system.

Demand migration is not supported on GPFS file systems. Copying a large file to a GPFS file system with insufficient space yields an out-of-space error message.

Hidden directories and files are included in automatic migration. Hidden objects can be excluded from automatic migration by adding the hidden objects to the exclude list in the dsm.sys file.

There is a potential impact on applications that depend on a timely response to write requests. The delay time depends on how fast objects are migrated from the file system to create free space and on the configuration of the space management client. For instance, if the HSM client is configured to require a backup before migration, the migration process can be delayed until the objects are backed up. To avoid a long delay, you must have enough eligible migration candidates.

On IBM® Storage Scale file systems, you can use the IBM Storage Scale policy engine to monitor space thresholds and search for migration candidates. In this case, the space monitor and scout daemons are disabled.

For information about configuring IBM Storage Scale integration with the space management client, see Technote 7018848.