Thanks to the help from the list I've successfully replaced part of
btrfs raid1 filesystem. However, while I waited for best opinions on the
course of actions, the root filesystem of one the qemu-kvm VMs went
read-only, and this root was of course based in a qcow2 file on the
problematic btrfs (the root filesystem of the VM itself is ext4, not
btrfs). It is very well possible that it is a coincidence or something
inducted by heavier than usual IO load, but it is hard for me to ignore
the possibility that somehow the hardware error was propagated to VM. Is
it possible?
No other processes on the machine developed any problems, but:
(1) it is very well possible that problematic sector belonged to this
qcow2 file;
(2) it is a Kernel VM after all, and it might bypass normal IO paths of
userspace processes;
(3) it is possible that it uses O_DIRECT or something, and btrfs raid1
does not fully protect this kind of access.
Does this make any sense?
I could not login to the VM normally to see logs, and made big mistake
of rebooting it. Now all I see in its logs is big hole, since, well, it
went read-only :( I'll try to find out if (1) above is true after I
finish migrating data from HDD and remove the it. I wonder where else
can I look?
--
With Best Regards,
Marat Khalili
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