Because of this, most RAID 5 setups include a RAID controller, both to reduce the time required, and to pre-acknowlege the receipt of proper data to be written to the drives momentarily. This takes some TIME to compute the check data on Write, and may take Time to check on Read. If any of the three are lost, the other two can (in theory) be used to recover the missing data for the third. RAID 5 gets its redundancy by calculating a permutation (XOR or Checksum or similar) of the bits in two blocks, and recording that as the third block.
And there is serious question about whether anyone should be using RAID 5.
