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.
Comments
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.