Various documents on Mirrored OS Drives suggest you can simulate the
failure of one of your mirrored pairs by marking one or more partitions
as "failed" with mdadm.
Indeed when I mark a drive as "failed", if I have the mdadm monitoring
daemon running, I get an email warning me that my RAIDS are degraded.
Also, I can reboot with only one drive plugged in and the OS comes up
fine (albeit degraded).
This gives me a REASONABLE degree of confidence that the Mirrored
Partitions will continue working okay if one drive should fail. However,
I would like to run a more definitive test.
I tried simply unplugging one drive from its power and from its SATA
connector. The OS didn't like that at all. My KDE session kept running,
but I could no longer open any new terminals. I couldn't become root in
an existing terminal that was already running. And I couldn't SSH into
the machine.
It was like I had an OS running on only a 1/4th of a cylinder. I
couldn't even make the OS cleanly shutdown or reboot.
I know that simply unplugging a drive is not the same as a drive failing
or timing out. But is there a more realistic way to simulate a failure
so that I can know that the mirror will work when it's needed?
Andy Liebman
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