The two sound very similar. I've been studying Bookkeeper this week to understand how it works and was excited to see the blogpost about LogDevice.
My understanding isn't fully there yet, but BookKeeper seems to have a more involved protocol versus LogDevice: ie it has fencing to ensure that only one writer is writing to a log at a time a 2-phase-commit-like protocol, and opening/closing of ledgers.
To me LogDevice's sequencer and epoch number sounds much simpler. Does BookKeeper achieve some more consistency or other guarantees that LogDevice doesn't by having a more involved protocol? How do the two compare in terms of goals/pros/cons/tradeoffs/usecases/etc?
(From reading the blog post it seems to me that in LogDevice an old sequencer could still be writing to LogDevice when a new one with a higher epoch number is also writing. As I understand it BookKeeper uses a CAS operation on metadata version number (like the epoch number of LogDevice) AND fencing on the storage nodes to make sure that only a single writer is writing at a time).