Most of the physical tapes used today for backup purposes are LTO tapes. The vendors are specifying a "native" and a "compressed" tape capacty. The "native" capacity is basically the amount of data the tape can hold without any compression. But as these devices are compressing the data, it is expected more than the native capacity will fit on the tape. That is why a specific compression ratio is assumed by the vendors to be able to specify the "compressed" capacity.
In a real-life situation, also with Data Protector, it's often seen that less than the compressed capacity is fitting on the tape. In some cases, it's even less than the native capacity. Why?
The first situation (less than compressed capacity) is rather easy to understand.
But if it is assumed the compression ratio will never be less than 1 and the meta-data written to the tape is also taken into account already then how is it possible to see less than the native capacity fit on the tape?
If a certain number of files and directories need to be backed up then it is clear there is no way of enhancing the compression ratio or decreasing the amount of meta-data. The backup speed, however, is something that may possibly be fine tuned by increasing the concurrency (multiple data streams to the same device; see Advanced device options) or by changing the backup path and/or the infrastructure (network, SAN, interfaces, different media agent client, ....). Write errors, if they occur, obviously need to get resolved on the hardware side by replacing a faulty device or tape (contacting harware support may be required).
Micro Focus Customer Care Specialist
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