[linux-lvm] Devices seen twice - how does LVM handle ?

[Rainer Krienke]

On Mittwoch, 10. September 2003 15:20, Luca Berra wrote:
> On Wed, Sep 10, 2003 at 03:04:25PM +0200, Markus Baertschi wrote:
> >For reasons too complicate to explain here our SAN configuration is
> >broken. The effect is that linux sees the san disks twice. The originally
> >
> >However, does LVM handles this situation (disks visible twice) nicely ?
>
> does not seem broken to me if you have two hba.
> lvm does not support multipath
>
> >or should I continue to use my workaround (pull a fiber) to make sure
> >the disks are visible only once ?
>
> it is not a nice workaround.
>
> >- Are there risks of corruption ?
>
> i don't think so.
>
> >- What happens if the path the LVM happens to use breaks, but the other
> >is still up. Will LVM handle fail-over ?
>
> lvm does not support multipath

It did not follow this discussion right from the start, so I might have missed 
something...

We are running 3 fileservers with raid devices attached by fibrechannel. Since 
each divice can be reached by 2 seperate io paths we are using a multipath 
setup based on the md interface (on top of the multipath md devices we 
finally run a software mirror (raid1)). This works just fine for our servers 
(running suse8.2) .  At the beginning we also had trouble with lvm1 since it 
was able to see the volume on different levels of abstraction: lvm scanned 
the real disks, it also scanned the md multipath metadevice and this probably 
led to the bad behaviour that whenever creating new logical volumes the 
complete configuration was invalid and so all data lost. 

We then changed to lvm2 since it has the ability to specify which devices to 
scan for lvm metadata and since then everything works fine.  

Rainer
-- 
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Rainer Krienke, Universitaet Koblenz, Rechenzentrum
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