because the OS did't cache the full ecc block (it views the block size as 2048 or 4096 bytes), and with scratched media 2 reads of the same ecc block aren't goi

because the OS did't cache the full ecc block (it views the block size as 2048 or 4096 bytes), and with scratched media 2 reads of the same ecc block aren't going to necessarily both succeed. simplistic case, imagine we have 1 ECC block of 16k, but we read at 2k, so we'll number the 2k blocks 0-7 T0 - read block 0, fails T1 - read block 1, succeeds! T2 - read block 2, fails T3-T7 repeat for blocks 3-7, all fail in practice if we read a 16k bock at T1, we would be golden (and finished). Instead we did 8 steps, and only got 1/8 of the data. This is becaue the OS doesn't have a concept of the hardware's ECC block size, so the optical hardware in a sense virtualizes it, and the OS will just keep on rereading the same ECC block on the media and possibly continue to get errors.