[linux-lvm] Device mapper does not really remove the references to removed LV.

[Germain Maurice]

Thanks for your answer Zdenek,

My cluster is in production and i know the virtualization solution we use is not optimal.
I will not programming a new daemon, but maybe a script that just do the job. The best way
to avoid any problem is to change my solution or deploy clvmd, i know.

For now, I just have to know how to proceed to avoid any problems.

So, before removing an LV, I think I have to do this :
- stopping the VM
- on every nodes : "lvchange -an /dev/VG/LV-to-remove"
- on one node : "lvremove /dev/VG/LV-to-remove"
- "vgscan" on every nodes.

And for creating :
- on the same node :
   - "lvcreate … /dev/VG/new-LV" 
   - "lvchange -ay  /dev/VG/new-LV" or "vgchange -ay"
- on the other nodes : 
   - "vgchange -ay"
- starting the VM on one node

For any LV modification :
- stopping the VM
- on every nodes : "lvchange -an /dev/VG/LV-to-remove"
- on one node : "lvmodify /dev/VG/LV-to-modify" and "lvchange -ay  /dev/VG/new-LV"
- "vgscan" on every nodes.
- starting the VM on one node (doing some stuff inside the VM)

Do you agree with that ?

I can do it manually because i don't have so much deployments to do.


Thank you for your help.



Le 15 mai 2012 à 10:12, Zdenek Kabelac a écrit :

> Dne 14.5.2012 19:37, Germain Maurice napsal(a):
>> Hi everybody,
>> 
>> I'm facing to some problems in my virtualization cluster and i need some help to prevent it occurring again.
>> 
>> I know that LVM is not cluster aware and we have to use it with lot of caution.
>> However, i have a shared LVM storage between 6 nodes. I use KVM hosts.
> 
> Hmm - if you are planing to build your own cluster - assuming you do not want to use lvm2 cluster support tools like clmvd - which needs advanced configuration) - you will need to write your own daemon, to watch out for locks and metadata changes.
> 
>> 
>> Two days ago i rebooted my whole cluster in order to get the same LVM metadata and the same dmsetup table over the cluster. That's ok.
>> 
>> "vgck SATA6To" is ok.
>> 
>> Right now, I have a problem when deleting an LV.
>> 
>> On the node where the VM lives, i did the lvremove command (lv name : SATA6To/vm-306-disk-3), i have a good state of LVM :
> 
> You need to propagate such change around your cluster by your daemon - and you have to be quite carefully where have you activated such LV before doing lvremove.
> 
> lvremove is simple command which does not communicate with other nodes in your cluster to let them know something has changed - so you might find some inspiration in CLVMD and it's locking technique to distribute locks around the cluster.
> 
>> 
>> Any idea how to clear all references to the LV previously removed ?
>> 
> 
> Before you remove LV on any node - you have to make sure all nodes deactivated such LV.
> 
> IMHO I'd suggest to use clvmd - instead of programming new daemon...
> 
> Zdenek
> 
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