Hello Tejun et al,

On 9/13/06, Tejun Heo <[EMAIL PROTECTED]> wrote:
Ric Wheeler wrote:
> (Adding Tejun & Greg KH to this thread)
Adding linux-ide to this thread.
>
> Leon Woestenberg wrote:
[--snip--]
>> In short, I use ext3 over /dev/md0 over 4 SATA drives /dev/sd[a-d]
>> each driven by libata ahci. I unplug then replug the drive that is
>> rebuilding in RAID-5.
>>
>> When I unplug a drive, /dev/sda is removed, hotplug seems to work to
>> the point where proc/mdstat shows the drive failed, but not removed.

Yeap, that sounds about right.

I suppose this is 'right', but only if we think of a hot unplugged
device as a failing device.

As in most cases we cannot tell if the hot unplug was intentional or
not (because we see a device disappearing from the phy and we have no
other sensory data available), assuming the drive 'fails' seems
reasonable.

>> Every other notion of the drive (in kernel and udev /dev namespace)
>> seems to be gone after unplugging. I cannot manually removed the drive
>> using mdadm, because it tells me the drive does not exist.

I see.  That's a problem.  Can you use /dev/.static/dev/sda instead?  If
you can't find those static nodes, just create one w/ 'mknod
my-static-sda b 8 0' and use it.

Yes, that works.

Also, replugging brings back the device as /dev/sda, indicating md is
no longer holding the internal lock.

Apart from persistent naming Ric mentioned above, the reason why you
don't get sda back is md is holding the internal device.  It's removed
from all visible name spaces but md still holds a reference, so the
device cannot be destroyed.

To me, this seems a bug, as the kernel already told everyone else
(userland) that it thinks the device is no longer there.

This contradicts the fact that the kernel itself has dangling references to it.

So, when a new device comes along, sda is
occupied by the dead device, and the new one gets the next available
slot, which happens to be sde in your case.

>> What is the intended behaviour of md in this case?
>>
>> Should some user-space application fail-remove a drive as a pre-action
>> of the unplug event from udev, or should md fully remove the drive
>> within kernel space??

I'm curious too.  Would it be better for md to listen to hotplug events
and auto-remove dead devices or is it something which belongs to userland?

...also considering race conditions between userland and kernel in that case...

My first thoughts would be that a unplugged device should be handled
differently than a device that failed in other senses, or at least
this should be considered by the kernel developers.

Thanks for the response so far, regards,
--
Leon
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