Re: removed disk && md-device

[David Greaves <david@dgreaves.com>]

Neil Brown wrote:
> On Wednesday May 9, bs@q-leap.de wrote:
>> Neil Brown <neilb@suse.de> [2007.04.02.0953 +0200]:
>>> Hmmm... this is somewhat awkward.  You could argue that udev should be
>>> taught to remove the device from the array before removing the device
>> >from /dev.  But I'm not convinced that you always want to 'fail' the
>>> device.   It is possible in this case that the array is quiescent and
>>> you might like to shut it down without registering a device failure...
>> Hmm, the the kernel advised hotplug to remove the device from /dev, but you 
>> don't want to remove it from md? Do you have an example for that case?
> 
> Until there is known to be an inconsistency among the devices in an
> array, you don't want to record that there is.
> 
> Suppose I have two USB drives with a mounted but quiescent filesystem
> on a raid1 across them.
> I pull them both out, one after the other, to take them to my friends
> place.
> 
> I plug them both in and find that the array is degraded, because as
> soon as I unplugged on, the other was told that it was now the only
> one.
And, in truth, so it was.

Who updated the event count though?

> Not good.  Best to wait for an IO request that actually returns an
> errors. 
Ah, now would that be a good time to update the event count?


Maybe you should allow drives to be removed even if they aren't faulty or spare?
A write to a removed device would mark it faulty in the other devices without
waiting for a timeout.

But joggling a usb stick (similar to your use case) would probably be OK since
it would be hot-removed and then hot-added.

David

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