On Jan 30, 2007, at 09:52, Luke Scharf wrote:
"Hey, I can take a double-drive failure now! And I don't even need to rebuild! Just like having a hot spare with raid5, but without the rebuild time!"
Theoretically you want to rebuild as soon as possible, because running in degraded mode (even with dual-parity) increases your chances of data loss (even though the probabilities involved may seem remote).
Case in point, recently at work we had a drive fail in a server with 5 +1 RAID5 configuration. We replaced it, and about 2-3 weeks later a separate drive failed. Even with dual-parity, if we hadn't replaced / rebuilt things we would now be cutting it close.
I understand all the math involved with RAID 5/6 and failure rates, but its wise to remember that even if the probabilities are small they aren't zero. :)
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