Re: A snapshot is not (really) a cow

[Peri Hankey <mpah@thegreen.co.uk>]

That looks like it.

The xen0 default kernel config used to build nbd as a module. That meant 
that there were no nbd devices available at boot or at any time until 
you explictly loaded the nbd module. So they weren't visible to the lvm 
code that scans block devices. With the nbd devices available, the lvm 
stuff starts happily scanning and rescanning all 128 of them.

So far I have managed to show this by inadvertently putting a syntax 
error in lvm.conf - my attempts to reject nb* and accept others 
continued to scan everything. But I think I'm on the right track.

Thanks
-- Peri

Wm wrote:

>On Mon, Sep 27, 2004 at 09:40:49AM +0100, Peri Hankey wrote:
>  
>
>>A further point - I mentioned in my last mail that attempts to access an 
>>nbd device start very early in the boot sequence. I now also notice 
>>after looking at several boot sequences that the first seems always to 
>>be an attempt to access nbd60, sector 0 (but the sector 0 may be a red 
>>herring).  I suspect something is trying to acccess block device 43,60 
>>hoping to find something other than a non-existent nbd device).
>>    
>>
>
>Could it be the lvm / device mapper initalistation scripts seaching for
>block devices with pvs on them?
>
>Can you have a look in /etc/lvm/lvm.conf in there you can tell
>lvm to only scan devices that you know might have pvs on them.
>
>
>bill
>
>
>  
>



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