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The FEC is implemented in the hard drive firmware. You're going to read back a full correct block or the whole block will fail. You're not going to read back a block with a single bit error, so it is insanity to protect against that at the FS level.

Also read up on RAID levels. RAID5/6 or ZRAID7 uses error correction not duplication.

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What about over the net? One of the listed strengths is its streaming capabilities, which implies sending it over the net. Error correction would be important there as well.

So you need something other than IP checksums, and whatever error correction is also operating in the layers below it?

I've downloaded and uploaded many files which have arrived incorrectly over the internet, so yes, if you truly want to prevent bitrot, you do want to add error correction.

This is a transport problem, however. Why not calculate the error correction codes on the fly? Why wast disk blocks?

Because you want to guarantee a certain error margin, regardless of the error detection & retransmit/correct capability of whatever networks/file systems/media it traverses in the interval till you want to read it.

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