3 ms·
Drive failure during a rebuild isn't a real concern unless 1) the rebuild takes time comparable to characteristic lifetime of the drive, which on average is >5
by effie 6y ago
Drive failure during a rebuild isn't a real concern unless
1) the rebuild takes time comparable to characteristic lifetime of the drive, which on average is >5years. Rebuild times are more in the realm of days, maybe coming to weeks with the proposed 100TB models. Still far from substantial probability of failure.
2) the drives are very old or have bad SMART data. Then the probability of drive failure and (array loss) shoots up.
What people often talk about regarding big drives and reliability concerns is probability of rebuild failure for RAID5, RAID6, i.e. some bit is read or written wrong and the array becomes inconsistent. This is much more probable but isn't really a big problem in practice because this can be detected and rebuild can be repeated.
- effie 6y agoOK the above isn't exactly correct in the last sentence. If there is URE due to medium error then we get a bad stripe and repeating rebuild will most often achieve nothing to remove it (although see SpinRite which can sometimes recover data from bad sectors). However, even if the bad sector can't be read, the "RAID failure" is still just loss of single or few sectors, which usually isn't a big deal. The array filesystem data is then best copied to a new array on new disks and then the old array discarded.