> I was told that if you lose one volume of a raid set you can replace > and the data will get rebuilt, but if you lose a second volume before > you get the first one rebuilt you will lose all the data -- > irretrievably! > Is this true?
Yes, for RAID 5. While the parity information *is* distributed, it's a one-dimensional distribution. When that second drive goes and the rebuild isn't yet complete, you're SOL. In RAID 0 (striping only), lose one and you're screwed. For RAID 1 (mirroring), they're mirrored pairs, so if you lose one and then another one, the data is gone and there's nothing to recover from. > Is there any reasonable way to get around it? Y-cabled parallel drive arrays like they use in telcom switches and nuclear explosion instrumentation, but the price tag is astronomical, so probably not in the "reasonable" class. 160G of that equipment is well over $750K. > Is there > a reasonable alternative to raid? AFAIK, no, not unless you happen to be the Sultan of Brunei and have a immense quantity of unused cash available with nothing better to do with it (and if you do, I'll be happy to give some of it a warm home...). - db
