On Tue, 11 Apr 2006 at 6:36pm, Andy Green wrote
Using CentOS on a server destined to have a dozen SATA drives in it. The server is fine, raid 5 is set up on groups of 4 SATA drives.
Today we decide to disconnect one SATA drive to simulate a failure. The box trucked on fine... a little too fine. We waited some minutes but no problem was visible in /proc/mdstat or in /var/log/messages or on the console.
I ran mdadm --monitor /dev/md0 and no problem was shown.
Did you try doing any I/O to the array? In my limited experience with software RAID, it won't notice a drive missing until it tries to do something with said drive.
To really test it, I'd disconnect the drive while you have something disk intensive running. I like http://people.redhat.com/dledford/memtest.html, which unpacks and then diffs multiple copies of the Linux source tree. It'll have the system stressed *and* let you know if there any problems with the array running in degraded mode.