On Tue, 15 Jan 2008, Erik Anderson wrote: > Not to get preachy, but this is the main reason to avoid RAID0 like the > plague. Yes, there are some instances where RAID0 is called for due to > performance needs, but that's surely not the case with an external > drive. If you want to use RAID0, it's *imperative* that you use some > sort of offline backup to CYA for instances like this. If I understand correctly, if the probability of failure of one drive in some time interval is 'p' and the drives fail independently, then with RAID0, the probability of catastrophic loss is roughly 2p [really 2p(1-p)+p², but the extra -p² is small enough that it can be ignored] because if either drive fails, you lose your data, but with RAID1, the probability of catastrophic loss is p² because both drives have to fail. So if the probability of failure this week is 1/1000, then with RAID0 you will be about 2,000 times as likely to lose all of your data as with RAID1. It's really worse than that though because with RAID0, loss of one drive means loss of data, but with RAID1, you have a chance to replace the first failed drive before the second one goes, so they have to fail in fairly rapid succession. You also have a chance to back up data through some other method while waiting to replace the first failed drive. Mike