[DRBD-user] Is there any problem using DRBD over LVM?

Denis Cardon denis.cardon at tranquil-it-systems.fr
Thu Nov 8 15:33:40 CET 2012

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

Le 08/11/2012 12:52, Felix Frank a écrit :
> Hi,
> On 11/08/2012 12:18 PM, "[SOLTECSIS] Carles Xavier Munyoz Baldó" wrote:
>> Hi,
>> We are creating a PROXMOX 2 cluster using DRBD and we have doubts about
>> which of the next options is better:
>> (A) DRBD over LVM.
>> (B) DRBD as a PV for LVM.
>> Which is the best option?
>> I remember that I have read that DRBD over LVM is not a recomended
>> configuration, but I don't remember why. I believe that I have readed
>> that in the DRBD documentation itself, but I'm not able to find it now.
>> Anyone knows if exists any kind of problem using DRBD over LVM?
> it does work :-)
> I'm not at all sure what's better performance-wise.
> If your backing device is an LV, you do incur a write penalty to all
> drbd interactions on both nodes.
> Still, that doesn't mean that the setup will be slower than the other
> way around.
> It's usually a good idea to make your own tests, hopefully with a most
> befitting workload.

I've been digging into this issue recently. There is some drbd 
documentation with this scenario 
(http://www.drbd.org/users-guide/s-lvm-lv-as-drbd-backing-dev.html), and 
I have done such setup in the past. It does work, but I was wondering if 
it is safe?

DRBD by default make use of barrier (unless no-disk-barrier is set with 
a BBU RAID backend), and such barrier where not correctly implemented in 
LVM before kernel 2.6.33. So I guess there are some cases where there is 
problems, eg. with software MD raid.



> Cheers,
> Felix
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Denis Cardon
Tranquil IT Systems
Les Espaces Jules Verne, bâtiment A
12 avenue Jules Verne
44230 Saint Sébastien sur Loire
tel : +33 (0)

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