drbd really is the best answer as its continuous in-order replication.
Assuming of course that you dont need any kind of performance from your filesystem drdb is indeed the answer.
ZFS snapshots can however be run on a per second basis which is quite neat! What ever you choose to do you would probably want to use mysql binary replication anyway so having a completely sync filesystem replica is probably not too much of a problem.
I must point out that virtualisation made these kinds of problems mostly go away (assuming of course that you have cash for some kind of High Availability iSCSI device or something.
-- john r pierce 37N 122W somewhere on the middle of the left coast
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