File checksums needed?
Posted Dec 6, 2008 18:57 UTC (Sat) by giraffedata
In reply to: Correctness
Parent article: Tux3: the other next-generation filesystem
A disk will happily write half a sector and scribble trash. Most times reading that sector will report a failure, but you only get reasonable odds.
Actually, I think the probability of reading such a sector without error indication is negligible. There are much more likely failure modes for which file checksums are needed. One is where the disk writes the data to the wrong track. Another is where it doesn't write anything but reports that it did. Another is that the power left the client slightly before the disk drive and the client sent garbage to the drive, which then correctly wrote it.
I've seen a handful of studies that showed these failure modes, and I'm pretty sure none of them showed simple sector CRC failure.
If sector CRC failure were the problem, adding a file checksum is probably no better than just using stronger sector CRC.
to post comments)