Handle clones
Posted by Sven Koester, Last modified by Andre Kuehnemund on 19 September 2012 14:21
|
|
Cloning is a mechanism to maintain a duplicate volume, thus increasing data availability. In case the original volume becomes unreadable, the data can still be recovered from its clone. PresSTORE supports pool cloning.
Customers who only have a single tape drive may want to consider archiving the same data twice. The resulting tapes won't be clones. However, just as with cloning, the benefit would be to have to tapes (or sets of tapes) of the same archived data. If one tape or tape set gets lost or becomes unreadable, one would still have the other tape or tape set to recover data from. | |
|
In addition to the backup job, there are several archive jobs. For the archive jobs, only the clone tape is removed and stored off site. The master tape remains in the library as long as we have space. Thus, over time, having two or more partitions will leave the tape library with lots of empty slots in one partition and very full in another partition. Because large tape libraries are licensed by the active slot, this approach would get very expensive, very fast. We needed a solution that optimized the capacity and drive usage of the tape library.
Our solution (for anyone facing this dilemma) was to make a copy of the database using the "Download support Data" feature. Then we run a SQL query against the database copy (never do this to your live database). The output of the query is then parsed by a shell script to find matching "copy of" records. Each pair of "copy of" records are split into two text files. Those text files form the "Master" and "Clone" tape lists. It is a bit of a process, but it gets the job done.
Is there a way to generate a clone afterwards? Or to declare a volume as a clone of another, and then use the re-generate function?
When using cloning the way it is meant to be used, P5 will write to both tapes simultaneously. When the first tape is full (doesn't matter which one of the two), the other tape will be closed as well. That way, both tapes end up being identical clones.