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by ChuckMcM
4615 days ago
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Was going to say the same thing, Dual drive failure on a RAID5 system with five 2TB drives is 1 in 12. With 3TB drives that goes up to 1 in 7. The underlying issue is that the uncorrectable read error rate is 1 in 10^15 bits, this is just physics (thermal noise, read/write signal loss, etc) But with 8b/10b encoding that is only 90TB worth of bits. Rebuilding a RAID group of 5 with four 2TB "good" drives (8TB of data to be read) you will see a failure in one of the other 4 drives 1 in 11.25 times. (90/8). With 3TB drives 1 in 7.25 times. Using simple mirroring you won't be able to re-silver a mirror 1 in 1:45 or slightly more than 2% of the time for 2TB drives. Dual parity, or triple mirrors (x3) are now the minimum bars for making storage reliable. |
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