Is DRBD the only viable block replication solution for Linux?

I've found myself needing redundant storage at a block level. File-level replication (Gluster, GFS, etc) does not work for my use case.

It looks like DRBD is the go-to solution for block replication. There don't seem to be too many other sane options. Have I failed in my research, or is DRBD the only game in town?

Yes, DRBD is the only replicated block device out there that can handle concurrent writes. If you plan to put a filesystem on top, it obviously needs to handle multiple writers as well, like GFS(2) and OCFS(2) do.

Please note that if you can afford higher levels of abstraction for redundancy, you'll likely be much, much happier with file-level semantics, so you should really think twice before going with block-level semantics. If you can't use higher levels of abstractions, but have money to throw at the problem, you can achieve significantly better performance with a good SAN.

But you probably know that already.

Well, there's also MARS (Light). According to the documentation this widely used at German provider 1&1