[DRBD-user] Fwd: Re: drbd stops sync on LVM

Eric Deschamps erdesc at free.fr
Wed Sep 8 17:07:07 CEST 2010

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Le 08/09/2010 17:00, Lars Ellenberg a écrit :
> On Wed, Sep 08, 2010 at 04:53:12PM +0200, Eric Deschamps wrote:
>> Le 08/09/2010 16:30, Lars Ellenberg a écrit :
>>
>>>
>>> See how not one of them references DRBD,
>>> but all directly use the lower level LVs directly?
>>>
>>> If you bybass DRBD, you cannot expect it to magically know
>>> about, and sync, your changes.
>>>
>>
>> The VMs are directly on LVs and LVs are the backing devices for DRBD
>> nodes, as in the user guide:
>> http://www.drbd.org/users-guide-emb/s-lvm-lv-as-drbd-backing-dev.html
>>
>> The sync works (actually, makes a snapshot) if I use drbdadm
>> invalidate-remote.
> 
> 
> Ok, I'll try again.
> You have:
> 
>  VM         [DRBD] -------- [DRBD] remote node
>   \          /
>    \        /
>  [logical volume]
> 
>  (DRBD does not see or know about any changes done by VM)
> 
> You need:
>              [VM]
> 	      |
>             [DRBD] -------- [DRBD] remote node
>             /
>  [logical volume]
> 
>  (DRBD sees every change done by the VM, and thus
>   has a chance to mirror the changes over).
> 
> Ok?
> 
> If you trigger a full sync in [what you have],
> of course everything that is in the LV is synced over.
> Though, if it is changed during that time directly from the VM,
> it will be inconsistent.
> 
> 
> 

OK, understood.

Many thanks again Lars!

Eric



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