I have heard stories of entire SANs failing so I would not advice trusting your SAN too much. For example there was a huge outage at a Swedish host caused by a

I have heard stories of entire SANs failing so I would not advice trusting your SAN too much. For example there was a huge outage at a Swedish host caused by a failed SAN, all data was lost so people had to use daily backups to restore. Replication can be done off-site so you at most lose a couple of seconds worth of data. I do not know anything about MySQL's replciation but my trust in PostgreSQL's is very high.