DPM show wrong media size

[Penko]

I saw a strange problem with HP Data Protector Manager
We have Ultrium 4 with 24 Tapes - 1.4 TB each.
Once the period of protection expires, the size of the tape shows as 800 GB instead of 1.4TB.
I installed all the latest patches.

Screenshot -> http://moiatblog.com/images/dpm-wrong-space.jpg

*Sorry for my English.

[thomasr · Accepted solution]

The native (uncompressed) capacity of these tapes is 800GB. The marketing folk like to say that the capacity is "1.6TB with 2:1 compression".

What it looks like to me is that you're seeing the actual use of the tape when it's full (1.4TB written with about 1.75:1 compression), but when the data on the tape is expired, the backup application doesn't know how much data *might* fit on the tape (because it doesn't know what compression will be until data is actually written), so it reports the native capacity.

I would not worry unless the same 1.4TB data set all of a sudden starts taking almost two complete tapes.