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03 Sep 2010

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	Handle clones

Solution 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 it's clone. PresSTORE supports two types of media cloning:

Pool cloning
Plan cloning

Pool cloning means that a second media is written in parallel at the same time. Pool cloning is set up via web interface in the page Media Pools->yourpool->General Setup. Check the box Clone data and select the drive(s) to use for the regular volume and for the cloned volume. Pool cloning is possible only in case you have at least two drives. Volumes generated by Pool cloning are identical, the same files are stored on both volumes. All volumes, the clone and the regular one belong to the same media pool.

Plan cloning is an elder variant of the cloning capability that has been kept in PresSTORE for compatibility. The use of this method is no longer recommended. Plan cloning can still be configured by selecting a second pool to clone to in the page Compatibility Options of the according Backup Plan or Archive Plan. The tapes are produced independent from each other; they are NOT identical, however the pools contain the same files. There is one exception: in case a file was modified between the original tape recording and the clone tape recording, the clone tape will contain a newer version of the file.
When using the Plan cloning, we recommend not to disable the Extension to create an unique index root path on the Index Options page of the Archive Plan. This extension, when active, allows to differentiate between the regular and the clone tape when restoring the data. In case the extension is disabled, the files are stored in the index like different versions of the same file. This means that when retrieving a file from such an archive, PresSTORE is selecting the clone or the regular volume by chance.

Broken, lost or worn-out volumes can be regenerated from their clones. In order to do so, label a new volume of the Media Pool where the broken/lost volume belongs to. Next, select the broken volume from the Volume Manager page and set it to disabled. Then select Edit->Regenerate Volume. In order to proceed, at least two drives are required: one for reading data from a cloned volume and one to write data to new volume. In case the clone volume was generated with the Plan cloning method, PresSTORE may request multiple volumes from the clone pool in order to regenerate the volume.

NOTE: regenerating a volume from Plan cloned volumes is supported only for archive volumes.

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16 Apr 2007 09:45 AM