Examples of how the Unitrends appliance uses the available space on archive tapes

This section contains figures to help you understand how available tape space is used during archive jobs. The figures specify how much space is available on tapes with status occupied; however, these numbers are included for explanatory purposes only. Due to limitations of tape media, the Unitrends appliance cannot display the amount of space available on an archive tape.

See the following topics for details:

     Successful archive job written across multiple tapes

     Failed attempt to write an archive set across multiple tapes

     Archive set written to as few tapes as possible

Successful archive job written across multiple tapes

This figure illustrates how an archive set with 100 GB of data is written across multiple tapes. The tape range for the job has been specified as 1 - 4. The job begins on Tape 1, which has a status of occupied and 40 GB of free space. The job uses this space, but it needs an additional 60 GB. This data would fit on Tape 2 or 3, both of which have status occupied. However, because all subsequent tapes used in a multi-tape job must have status empty, the appliance does not use Tape 2 or 3. Instead, it completes the job by writing the remaining 60 GB to Tape 4, which has the status empty.

UseCase8.png

 

Failed attempt to write an archive set across multiple tapes

This figure illustrates how an attempt to write a 75 GB set across multiple tapes could fail. The tape range for the job has been specified as 1 - 5. The job does not use Tape 1 because it has a status of full. Tape 2, with status occupied, has 50 GB available, so the job uses this space. To complete the job, the appliance must locate an additional 25 GB of usable space. Tapes 3 and 5 each have enough space to write the rest of the set, but the appliance cannot use them to complete the job because their status is occupied. The appliance searches for a tape with status empty, and because it cannot find one in the specified range, the job fails. However, because part of the job was written to Tape 2, the resulting archive set contains a subset of the desired backups, and it is possible that these backups can be restored.

UseCase7.png

 

Archive set written to as few tapes as possible

This figure illustrates how the Unitrends appliance uses as few tapes as possible to write a 75 GB archive set across multiple tapes. The tape range for the job has been specified as 1 - 10. The job does not use Tape 1 or 2 because both have a status of full. Tape 3, with status occupied, has 15 GB available, so the job uses this space. The remaining 60 GB is written to Tape 10, with status empty.

The combined amount of free space on Tapes 4 - 9 is 60 GB, but if the appliance used this space for the job, it would need a total of seven tapes for the archive set. Because it uses Tape 10 instead, the job requires only two tapes for the entire archive set. To restore this archive set, only tapes 3 and 10 are required.

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