2012-01-15 20:43, Gary Mills пишет:
On Sun, Jan 15, 2012 at 04:06:33PM +0000, Peter Tribble wrote:
On Sun, Jan 15, 2012 at 3:04 PM, Jim Klimov<jimkli...@cos.ru>  wrote:
"Does raidzN actually protect against bitrot?"
That's a kind of radical, possibly offensive, question formula
that I have lately.


Yup, it does. That's why many of us use it.

There's actually no such thing as bitrot on a disk.  Each sector on
the disk is accompanied by a CRC that's verified by the disk
controller on each read.  It will either return correct data or report
an unreadable sector.

What about UBER (uncorrectable bit-error rates)?
For example, the non-zero small chances of another block contents
matching the CRC code (circa 10^-14 - 10^-16)?

If hashes were perfect with zero collisions, they could be used
instead of original data and be much more compact, and lossless
compression algorithms would always return smaller data than
*any* random original stream ;)

Even ZFS dedup with 10^-77 collision chance proposes a mode to
verify-on-write.

>  There's nothing inbetween.

Also "inbetween" there's cabling, contacts and dialog protocols.
AFAIK some protocols and/or implementations don't bother with the
on-wire CRC/ECC, perhaps the IDE (and maybe consumer SATA) protocols?


Thanks for replies,
//Jim Klimov
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