Back in TSM v6.2 and earlier versions, backing up the TSM database (DB) required just 2 things to think about: the device class to be used and the type of backup you wanted. Of course, you can still use this, but since TSM v6.3 different methods were introduced to handle the increased TSM DB backup size. Typically, the size of the TSM DB will increase noticeably when using TSM native deduplication (client-side or server-side). All that metadata about all those chunks, pointers, dereferenced chunks, etc., etc. eventually needs to be stored somewhere. The increased TSM DB size also increased the space requirements for the DBB’s.
Two of the methods introduced:
Introduced in v6.3.0, and named ““Multistream database backup and restore processing”. The NUMStreams specifies the number of parallel data movement streams to use when you backup the DB. The default is 1, the maximum is 4. This will not reduce the space requirements for the DBB’s, but it might improve the overall time a DBB take. Typically you should only use this if your TSM DB is big enough. Meaning: multistream backups will not win you that much time with a small TSM DB, but the concurrent data stream will cause you to lose volumes which are not fully utilized. As always, there is a tradeoff to consider.
The 12th edition of the well known European TSM Symposium was announced a while ago. This time the theme is “Tivoli Storage Manager: Promising Future”.
From the TSM Symposium 2015 website:
The TSM Symposia cover a wide variety of Tivoli Storage Manager (TSM) related topics and particularly thinking about Benefit from Innovation for new and changed functionality expected to come in TSM over the next couple of years. The well-established TSM-Symposium is hosted by Guide-Share-Europe and the University of Cologne. It will take place from Tuesday 22th September 2015 to Friday 25th September 2015 in the Westin Bellevue Hotel in Dresden, Germany.
It will have been two years since the last symposium in Berlin and there will be plenty of TSM related topics to talk about.
The behavior described in the article can be applied for backups and archives. Backups will be used throughout the text as an example.
The TSM server reads and writes predominantly in 256 KB blocks for sequential access pools. The problem described here does not exist in such extent on a random access disk storagepools, which uses a block size of only 4 KB.
TSM’s logical during transactions of backing up and restoring data, is that multiple smaller files will be put together into an aggregates. When backing up just a small, single file per transaction/command, it will be a block of 256 KB per very small file. The minimum unit is 1 block of 256 KB, whether the originating file is for example 1 KB or 64 KB.
This information is meant to discuss some useful TSM server parameters in relation to deduplication. It is by no means an in-depth explanation about TSM’s deduplication, or even deduplication in general.
If you have a Virtual Tape Library (VTL) which can (in-line) deduplicate the stored data, e.g. IBM’s ProtecTIER, you most likely want to use this built-in hardware deduplication functionality. As you are aware, you can also choice to use TSM’s native deduplication. This means deduplication on the TSM application level and it is available for client-side and server-side, or even a combination of both.
There might be problems when one is trying to deduplicate very large objects, because this will result in many, many chunks, associated metadata, server processing, etc. Sometimes it might be beneficial to just exclude very large objects from deduplication altogether.