A failed drive causes system to hang

[Radio młodych bandytów]

Seeing a ZFS thread, I decided to write about a similar problem that I 
experience.
I have a failing drive in my array. I need to RMA it, but don't have 
time and it fails rarely enough to be a yet another annoyance.
The failure is simple: it fails to respond.
When it happens, the only thing I found I can do is switch consoles. Any 
command fails, login fails, apps hang.

On the 1st console I see a series of messages like:

(ada0:ahcich0:0:0:0): CAM status: Command timeout
(ada0:ahcich0:0:0:0): Error 5, Periph was invalidated
(ada0:ahcich0:0:0:0): WRITE_FPDMA_QUEUED

I use RAIDZ1 and I'd expect that none single failure would cause the 
system to fail...
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