If it's using block level replication, how does it offer instant
recovery on filesystem corruption? Does it track every block written
to disk, and can thus roll back to effectively what was on disk at a
particular instant in time, so you then just remount the filesystem
and the replay of the journal should restore to a good state?
Yes. I may be wrong but to my understanding at least NetApp has this
capability.
With file based replication, about your only way of failure is the
replication software going crazy blowing both sides away somehow,
which given that the protocol is strictly designed to be one way,
seems extremely unlikely that anything will happen to the master side.
I agree of course about avoiding SPOFs, but I do like a multi-tiered
approach, I mean multiple lines of defense. I use SAN for its speed,
reliability, and ease of administration, but naturally I replicate
everything on the SAN and have "true" backups as well.
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