Images not compressing

[salmon]

I'm creating some images of hdd's that were in my raid 5 array but the are not compressing r-studio says they will be about 600gb but after the image process finishes they are actually abot 1.3tb is this a demo limitation or is there some other reason they are not compressing?

Any help would be greately appreciated.

[Alt]

Most likely this is data on disk that's hard to compress.