[dm-devel] Device removal handling

[Hannes Reinecke]

On 07/11/2011 05:08 PM, Phillip Susi wrote:
> On 7/10/2011 6:03 PM, Alasdair G Kergon wrote:
>> (But devices should be removed from the top down, obviously, and if
>> it's your main filesystem, you could e.g. set up a ramdisk do do
>> this from.)
>
> I disagree. Right now dmraid relies on doing this, but this is not
> possible if it is not aware of the higher level mappings because
> they were created by kpartx. LVM and multipath will have the same
> problem if kpartx recognizes partitions contained within an LV.
>
> Hardware removal also necessitates bottom up removal, since the
> initial event comes from unplugging the hardware at the bottom of
> the stack. The system needs to propagate notification of that up the
> stack so that the higher layers can react appropriately and release
> the removed lower layer device.
>
Yes.

I've been facing this problem for a long time now;
eg if you're having a dm-mirror with one leg local and another one 
on iSCSI. Try shutting down iSCSI here with LVM going bonkers ...

I wouldn't mind replacing a failed device with an error target.
What I would mind is to having to code that logic into each and 
every subsystem which might find itself running underneath 
LVM/device-mapper.

What I would like to see is this logic being pushed into
eg dmsetup, so that one call to dmsetup would be sufficient to 
achieve this. And without heavy parsing of arguments etc.
Something like 'dmraid replace error' would be cool.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
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