[PVE-User] DRBD confusion in PVE wikki docs.

Muhammad Yousuf Khan sirtcp at gmail.com
Sun Jul 22 09:51:06 CEST 2012

On Sun, Jul 22, 2012 at 3:34 AM, THe_ZiPMaN <flavio-pve at zipman.it> wrote:
> On 07/21/2012 07:37 PM, Muhammad Yousuf Khan wrote:
>> here is the proxmox official wikki doc.
>> http://pve.proxmox.com/wiki/DRBD
>> i agree with Robert, what document saying is ,
>> it suggest us to create two volume r0 and r1
>> on node1 we use r0
>> and on node2 use r1
>> if split brain occurred then we dont have to shift whole data we just
>> discard the old data from victim node and resync the drbd data.
>> for instance in my confusion case if we discard the data from node1 r1
>> and node2 r0
>> in case of split brain. so the concept of saying it will take few
>> minutes as it updates only the changes, doesn't fit in the scenario
>> and making me confuse.
> If you fall in a split brain condition with drbd but on one node there
> were no VMs running, the data on that drbd device will be intact and
> will be a "snapshot" in the instant when the SB occurred (noone wrote on
> it after that moment).
> In this case you don't need to scratch the content of the volumes,
> because the data is consistent. You simply reconnect the device to it's
> primary and it will resync copying the data written after the S.B. occurred.
> Instead in the case where you have only one drbd device and 2 node that
> write on it, both the copy of the device contains fresh data and so you
> must do a manual merge. After that a full resync (or better the
> re-creation of the drbd device) must take place.

in shared Proxmox doc, in section "Recovery from split brain when
using two DRBD volumes"

drbdadm secondary r1
drbdadm -- --discard-my-data connect r1
on nodeB
drbdadm connect r1

why discarding the data here ? because we are using only one DRBD
device on one node. (as you said there is no need to scratch the data)

> --
> Flavio Visentin
> A computer is like an air conditioner,
> it stops working when you open Windows
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