removed disk && md-device

[Bernd Schubert <bs@q-leap.de>]

Hi,

we are presently running into a hotplug/linux-raid problem.

Lets assume a hard disk entirely fails or a stupid human being pulls it out of 
the system. Several partitions of the very same hardisk are also part of 
linux-software raid. Also, /dev is managed by udev.

Problem-1) When the disk fails, udev will remove it from /dev. Unfortunately 
this will make it impossible to remove the disk or its partitions 
from /dev/mdX device, since mdadm tries to read the device fail and will 
abort if this file is not there.

Problem-2) Even though the kernel detected the device to not exist anymore, it 
didn't inform its md-layer about this event. The md-layer will first detect 
non-existent disk, if a read or write attempt to one of its raid-partitions 
fails. Unfortunately, if you are unluckily, it might never detect that, e.g. 
for raid1 devices.

I think there should be several solutions to these problems.

1) Before udev removes a device file, it should run a pre-remove script, which 
should check if the device is listed in /proc/mdstat and if it is listed 
there, it should run mdadm to remove this device from the.
Does udev presently support to run pre-remove scripts?

2.) As soon as the kernel detects a failed device, it should also inform the 
md layer.

3.) Does mdadm really need the device?


Thanks,
Bernd


-- 
Bernd Schubert
Q-Leap Networks GmbH

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