Jim,
If these are SCSI disks, removing power can cause a MULTITUDE of problems
you won't see if the SCSI connection to a drive fails. Unless the drives
and controller aren't the original SCSI 1 8 bit bus, the termination has
power supplied by the drive. Removing the power kills the termination and
will lleave the bus in an undetermined state, with an unknown load on the
bus as well. I am going to place a guess and assume the 2nd drive that got
kicked was the next furthest drive away from the controller than the one
you unplugged. This would be expected.
If you power on the drives again and boot linux, it SHOULD correctly
restore the data... that is unless the raid was active when you unplugged
the drive, as SCSI drives have a large RAM cache that probably got
corrupted, and the data was never written to the 2 drives.
At 04:14 PM 12/31/1999 +0000, you wrote:
>I've been experimenting with my 4 disk Raid5 setup for a few weeks now and
>been impressed - so far.
>
>Today, I sucumbed to the temptation of of simulating a disk failure (or
>more accurately a power supply failure to a disk), by 'hot' unplugging its
>power lead. Nothing appeared to happen at first - mdstat reported that all
>disks were working. Then the system stopped responding to console commands
>- not even to a shutdown.'Never mind' I thought, I'll power cycle and when
>it fires up again the array will get reconstructed and all will be fine.
>However, on restarting, md reported that _2_ disks were non-fresh and were
>kicked from the array. This left only 2 disks for reconstruction - and the
>system gave up with a kernel panic. I'm now left with a system that I
>can't do anything with except a reinstallation from scratch.
>
>Where did I go wrong - what strategy should be adopted in such a
>situation? It seems to me that cutting the power to a disk is a reasonable
>test - simulating a faulty connection. Should I have waited longer before
>shutting the power off to the system - and was this the reason that the
>2nd disk went down? If I'd had a spare disk in the array, would it have
>reconstructed O.K.?
>
>Now - this is the interesting one - if the system had _not_ been Raid5 I
>could probably have done the same thing and still ended up with a useable
>system. In likelyhood, all that would have happened is that the fs would
>have been marked as dirty and a fschk carried out at next reboot. This
>suggests that Raid5 _can_ be more fragile than a non Raid setup.
>
>Regards: Jim Ford
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David Cooley N5XMT Internet: [EMAIL PROTECTED]
Packet: N5XMT@KQ4LO.#INT.NC.USA.NA T.A.P.R. Member #7068
We are Borg... Prepare to be assimilated!
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