some research

[Jose M. del Rio]

Thanks to everybody.
After some research, I've found the following information sources:
- STM gives information about available capacity ant compression ratio
- ioctl(SIOC_CAPACITY): the lba field of the struct capacity is an estimate of the available capacity
- ddsinfo reports available capacity and compression ratio.
The problem is STM, SIOC_CAPACITY and ddsinfo give different responses for available capacity. I know they're all estimates but why so different?
And talking about compression, I supose the "Kbytes to Tape" report of the ddsinfo tool computes the real bytes written to tape, but it is rather different than the decrease of available capacity reported by STM, SIOC_CAPACITY and ddsinfo. Why?
Any suggestion?
Thanks in advance.
Regards.