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I would say ZFS would be a lot closer to NetApp.

For Isilon, a better comparison would be Ceph. With Ceph you can have a cluster of 10s or 100s of servers, and you can lose 1 disk, or 1 server, or 1 rack or servers and it will recover very quickly.

As long as your minimum requirements for your type of replication or erasure coding profile are satisfied, your data stays safe and available.

RAIDZ2 / RAID6 (through linux md-raid, or anything else) both handle the 'lose 2 out of N+2 disks' case.

If you want something that deals with multiple tiers of fault tolerance, you should be looking at distributed filesystems (eg. Ceph) rather than single-system filesystems like ZFS and btrfs. Also keep an eye out for erasure coding as a keyword, since that usually implies more control over the degree of redundancy than a handful of RAID levels.

raidz2 for RAID6 like support where 2 disks can die.