Improved Capacity and Transfer rate
Capacity of course doubles with every new release of LTO . LTO-8's 12TB native is double the 6TB native of LTO-7 Media. Apart from capacity the performance has to be increased, so that the tape drive can write faster to the tapes. Compared to LTO-7, there is a 20% increase in the performance too.Capacity and transfer rates - both are improved with each new generation tape .
BaFe and TMR make it possible
Earlier generation of LTO tapes used Metal particle technology that maxed out around LTO-5. HP still kept shipping LTO-6 on Metal particle technology, whenever other manufacturer switched to BaFe Technology ( Though recently Quantum also switched to Metal particle on their LTO-6 media probably to save cost).Form LTO-7 onwards there was no doubt that only BaFe (Barrim Ferrite) could achieve the kind of areal density required for future capacities. However with LTO-8, you would need an even smaller tape head to read and write at an even small scale. The new TMR (Tunneling Magnetoresistive) drive heads make it possible to achieve the areal density required to achieve 12TB on a single tape.
LTO-7 Compatibility with a new Capacity
Every generation of new LTO tape drive is backward compatible to 2 previous generations of Media. For Example LTO-7 was read write compatible with LTO-6 media and read only compatible with LTO-5 media. However with LTO-8, for the first time the LTO-7 media is not only compatible but can be formatted to LTO-8 Type M format with 50% advance in capacity.What is means is that you can not only read/write on your earlier 6TB LTO-7 used media, but you can also format your previously unused LTO-7 media to LTO-8 type M media and enjoy 9TB native.
This is similar to IBM 3590 and 3592 tapes where the same tape could be used with different drives to yield different capacities.