Considerations for backing up file systems that are managed with IBM Storage Protect for Space Management

When IBM Storage Protect for Space Management is used to migrate data to secondary storage pools (for example, tape volumes), this migrated data might need to be recalled to disk if the file becomes a backup candidate due to certain changes a user may apply to it.

Recall will automatically occur synchronously if the user attempts to change the file data. However, no synchronous recall occurs in the following scenarios:

• If a user changes the owner, group, mode, access control list, or extended attributes of the file.
• If the user renames the file or any of the parent directories of the file.

Any of these changes, however, does make the file a candidate for the next mmbackup invocation. When mmbackup supplies the path to a migrated file to IBM Storage Protect for backup, synchronous recall will occur. This can lead to a "Recall Storm" in which tape library and IBM Storage Protect server resources become overburdened handling many simultaneous recall requests. Disk space is also consumed immediately by recalled data. These are undesirable outcomes and can interfere with the normal processing of the customer's workload.

Since mmbackup is able to discern that the data was migrated for such files, it will defer the backup, and instead append a record referring to the file's path name into a special file in the root of the file system, or fileset in the case of fileset-level backup. This list can then be used by the system administrator to schedule recall of the deferred files data to permit the backup to occur on the next invocation of the mmbackup command. By deferring the recall to the system administrator, mmbackup prevents unexpected, excessive tape library activity which might occur if many such migrated files were nominated for backup due to user actions such as renaming a high level directory or changing owner, group, or modes on many files.

The system administrator must schedule the recall for the migrated objects omitted by mmbackup according to the availability of tape and disk resources in the cluster. For information about optimized tape recall, see Optimized tape recall processing in IBM Storage Protect for Space Management documentation.