I contacted their support and was told that currently none of my slices are on the same machine. Also, they have a policy of never putting the same customer on one machine more than once, so in theory all future slices would be on different machines as well.

Either way they don't provide much in the way of disk storage. Even their largest plan only has some half-terabyte, which is not nearly enough for backups. What's state of the art on backup, Bacula still?