External storage pools

When you initially create a file, GPFS™ assigns that file to an internal storage pool. Internal storage pools support various types of online storage. To move data from online storage to offline or near-line storage, you can use external storage pools.

External storage pools use a flexible interface driven by GPFS policy rules that simplify data migration to and from other types of storage such as tape storage. For additional information, refer to Policies for automating file management.

You can define multiple external storage pools at any time using GPFS policy rules. To move data to an external storage pool, the GPFS policy engine evaluates the rules that determine which files qualify for transfer to the external pool. From that information, GPFS provides a list of candidate files and executes the script specified in the rule that defines the external pool. That executable script is the interface to the external application, such as IBM Spectrum Protect™, that does the actual migration of data into an external pool. Using the external pool interface, GPFS gives you the ability to manage information by allowing you to:

Move files and their extended attributes onto low-cost near-line or offline storage when demand for the files diminishes.
Recall the files, with all of their previous access information, onto online storage whenever the files are needed.

External pool requirements

With external pools, GPFS provides metadata processing and the flexibility of using extended file attributes. The external storage manager is responsible for moving files from GPFS and returning them upon the request of an application accessing the file system. Therefore, when you are using external storage pools, you must use an external file management application such as IBM Spectrum Protect. The external application is responsible for maintaining the file once it has left the GPFS file system. For example, GPFS policy rules create a list of files that are eligible for migration. GPFS hands that list to IBM Spectrum Protect which migrates the files to tape and creates a reference file in the file system that has pointers to the tape image. When a file is requested, it is automatically retrieved from the external storage pool and placed back in an internal storage pool. As an alternative, you can use a GPFS policy rule to retrieve the data in advance of a user request.

The number of external storage pools is only limited by the capabilities of your external application. GPFS allows you to define external storage pools at any time by writing a policy that defines the pool and makes that location known to GPFS. External storage pools are defined by policy rules and initiated by either storage thresholds or use of the mmapplypolicy command.

For additional information, refer to Working with external storage pools.