zfs.rent is in the wrong location and I can't see anything about zfs send/receive support on rsync.net. What kind of VPS product has multiple redundant disks attached? Aren't they usually provided with virtual storage?

It's documented here: https://www.rsync.net/products/zfsintro.html

Do note the 5 TiB minimum order for it though, it's not something that's enabled on other accounts.