..
That's exactly the worry.
If anyone want's to take a crack at testing some of the more likely
fail paths there, just introduce a media error onto a SATA disk
that's buried at the bottom of a stacked RAID1 over RAID0 over LVM,
with XFS and nfsd on top.
Or something like that.
And then experiment with corrupting meta data rather than simply file data.
How-to introduce a media error? hdparm --make-bad-sector nnnnnn /dev/sdX
This catches the most likely (IMHO) failure scenarios,
but still comes nowhere near 100% code coverage. :(
Cheers
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