Under these conditions, the MTTF of a group of disks is given by
MTTF_Group = (MTTF_Disk/G+C)*(1/Probability of another failure
in the group before repair)
The average number of failures for a single disk in the group is given by
The authors show that these facts leads to the following calculation of the MTTF for a RAID array:MTTR/(MTTF_Disk/Number_of_disks_remaining_in_the_group)
MTTF_RAID = (MTTF_Disk)2/((D+C*nG)*(G+C-1)*MTTR)
What does that mean?
Bit 1 stores parity for bits 1, 3, 5, 7, etc.
Bit 2 stores parity for bits 2, 3 and 6, 7, and 10, 11, etc.
Bit 4 stores parity for bits 4, 5, 6, 7, and 12, 13, 14, 15, etc.
It three or more errors occur in this situation, the problem will be incorectly diagnosed.