On Wed, 6 Aug 2025, John Stoffel wrote:
"Mikulas" == Mikulas Patocka <[email protected]> writes:
The problem is that the raid1 implementation may freely choose which leg
to read from. If it chooses to read from the non-corrupted leg, the
corruption is not detected, the number of mismatches is not incremented
and the test reports this as a failure.
So wait, how is integrity supposed to work in this situation then? In
real life? I understand the test is hard, maybe doing it in a loop
three times? Or configure the RAID1 to prefer one half over another
is the way to make this test work?
Linux needs an optional parameter to read() syscall that is "leg index"
for the blk interface. Thus, btrfs scrub can check all legs, and this
test can check all legs. Filesystems with checks can repair corruption
by rewriting the block after finding a leg with correct csum.
This only needs a few bits (how many legs can there be?), so can go in
the FLAGS argument.
