> > i would think this is acceptable. at these low levels, something > > else is going to get you -- like drives failing unindependently. > > say because of power problems. > > 8% rate for an array rebuild may or may not be acceptable > depending on your application.
i think the lesson here is don't by cheep drives; if you have enterprise drives at 1e-15 error rate, the fail rate will be 0.8%. of course if you don't have a raid, the fail rate is 100%. if that's not acceptable, then use raid 6. > > so there are 4 ways to fail. 3 double fail have a probability of > > 3*(2^9 bits * 1e-14 1/ bit)^2 > > Why 2^9 bits? A sector is 2^9 bytes or 2^12 bits. cut-and-paste error. sorry that was 2^19 bits, e.g. 64k*8 bits/byte. the calculation is still correct, since it was done on that basis. > If per sector recovery is done, you have > 3E-22*(64K/512) = 3.84E-20 i'd be interested to know if anyone does this. it's not as easy as it would first appear. do you know of any hardware or software that does sector-level recovery? i don't have enough data to know how likely it is to have exactly 1 bad sector. any references? - erik
