A bad drive caused i/o errors, but no notifications were sent out
because "btrfs dev stats" fails to increase the error counter.
When checking dmesg, looking for something completely different, there
were some error messages indicating that this drive is causing i/o
errors and may die soon:
BTRFS info (device sda3): read error corrected: ino 194473 off 2170880
But checking the stats (as generally recommended to get notified about
such errors) claims that no errors have occurred (nothing to see here,
keep moving):
# btrfs dev stats / | grep sda3 | grep read
[/dev/sda3].read_io_errs 0
Why?
Isn't that the most important feature of a RAID system - to get notified
about errors, to be able to replace such a drive...?
The fs is mirrored, so those errors didn't cause any data loss.
# uname -sr
Linux 5.2.7-100.fc29.x86_64
# btrfs --version
btrfs-progs v5.1
