28.04.2016 19:02, Paul Groves пишет:
Not sure what you are doing, but hardware compression is transparent to tar. It has no idea how much data is on the tape or how much physical space it taking up.
Suspected as much. Thanks Greg.
Does anyone know how can I check the real size of the data on the tape?
Also, I have tried running a backup until the end of tape message:
I am using an LTO3 tape which is 400GB native (up to 800GB) so I would expect somewhere between these values. The directory contains many un-compressed media files so should be compressible, and it is only 368GB in size. It stops at around about 250-300GB mark by my estimation, which was my original problem. It isn;t even using anywhere near it's native size.
Amount of data that fits on tape depends on too many factors. For well compressible data and when data could be streamed I have often got much better results than 2:1. Minimal speed that is required to keep LTO3 in streaming mode is around 27MB/s. If your application cannot keep up with it, your tape consists more of gaps than actual data.