Recalling migrated files overview

You can recall a migrated file to your local file system from IBM Spectrum Protect server storage either selectively or transparently. Files are recalled in either normal, partial, or streaming mode.

Selective recall returns specified, 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.

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, you change how the space management client recalls a migrated file.

Normal recall mode 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 IBM Spectrum Protect server storage remains valid. The local copy is premigrated.

Optimized tape recall optimizes the tape access during a recall of a list of files. Files indicated with the filelist option to the dsmrecall command are recalled in an order that optimizes tape access. The recall order minimizes tape mount and unmount operations and minimizes tape seek operations.

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

Partial file recall mode recalls a portion of a migrated file and is valid only for IBM Spectrum Scale systems. A partial recall avoids recalling an entire file, when only a small portion of the file is required by an application. The space management client intercepts a read request for a file configured for partial file recall. The space management client then calculates 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.

Streaming recall mode enables or disables an asynchronous 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.