File Server Replication - How many, when?

Many file server systems introduced replicated filesystems around 3 years ago... Perhaps. Simple hardware solutions like disk mirroring solve a lot of the reliability problems much more easily. Also, at least in a stable world, keeping your file server up is a better way to solve the problem. Optimistic vs. Pessimistic replica consistency control: Pessimism says, ;SPM_quot;inconsistency is so intolerable that we are willing to take expensive measures (like obtaining remote locks) to prevent it from occurring.;SPM_quot; Optimism says, ;SPM_quot;inconsistent concurrent update is so rare in practice that it makes more sense to detect it and fix it up when it does occur than it does to go to great expense to prevent it.;SPM_quot; It sort of parallels deadlock detection vs. prevention. It seems that there is no right answer, but rather situations where one is best and situations where the other is best. So far, however, the conservative (pessimistic) approach (primarily inherited from the distributed database arena) has been most common.