Question & Answer
Question
Is a specific storage pool required to keep directory information on disk?
Answer
The DIRMC option had a big impact on restore performance in earlier versions of Tivoli Storage Manager (pre V3), where directories were restored first, followed by the files. It was therefore an advantage to have directory information cached so that it was permanently on disk, and best practices design was to create small storage pools specifically for directories. The DIRMC directive in the client options file was used to bind directories to a management class pointing to this storage pool.
Restore processing has changed since then: during the process directories will be created with default attributes and the correct attributes and ACL information is applied once the data is read from the media. Therefore the original reason to cache directories on disk no longer applies.
Nevertheless, the DIRMC option is still useful. If you do not specify this option to associate a management class with directories, the client, during backup, uses the management class in the active policy set of your policy domain with the longest retention period, which could point to a storage pool on tape. This might result in unwanted mount requests during backup/restore.
Having the DIRMC point to a disk storage pool separate from the backup objects might cause the symptom as described with technote swg21247892 (Unexpected high number of EndTxn processing during back up, see link section below)
Note: APAR IT01994 documents an issue where the classic restore order for objects is not optimized. Under this condition you might see multiple mounts for the same volume. See link section for a link to the APAR details.
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Modified date:
17 June 2018
UID
swg21669468