When you try to compress highly compressed or random data the size expands.

At least on the LTO tape drives I have used, will disable compression if the size is larger in an adaptive way.

As tape read and write speeds depend on data size, it is still worth the effort to try and opportunistically compress data on drive.

As this can usually be done without stopping or slowing the tape, there really isn’t much of a downside.

As for the compressed capacity, that is just 30+ years of marketing conventions, which people just ignore as it has always assumed your data was 2:1 compressible.

Native is iirc 30TB - they quote compressed capacity but eh that's very much going to depend on what you are storing and how compressible it is.

And you'll have a rough idea what it is you are going to be storing and how compressible it is if you spending that kind of money.

It's marketing and a little skeezy to quote it and I bet they have some justification for why they arrived at 2.5:1 compression.

EDIT: Yeah it's 30TB - been many years since I had anything to do with LTO but they use a modified version of LZS called SLDC so it's that that they are assuming will get 2.5:1 on "random enteprise data that isn't already compressed" the 2.5 threw me as well because that used to be 2:1 so either they improved SLDC or thought they could wing it - looks like that switched between LTO-5 and LTO-6.

File compression requires additional storage, memory and processing power. Why bother if the tape appliance already handle it ? Data is unusable in compressed format and is hard to deduplicate. Also, often, there is already compression at the storage array level but the data is decompressed when read.