[DRBD-user] Split brain auto recovery with DRBD9

Digimer lists at alteeve.ca
Tue Mar 1 18:07:45 CET 2016

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

On 01/03/16 09:43 AM, Mark Wu wrote:
> Hi guys,
> According to
> http://drbd.linbit.com/users-guide-9.0/s-dual-primary-mode.html,
>  DRBD-9.1 will support multiple primaries.  I am wondering if it can
> also enhance the auto reovery from split brain. It seems that currently
> we don't have a good solution of recoverying from split brain without
> data loss when dual primary is configured. I think it will be good to
> have a policy to merge all up-to-date data. 
> I am considering to build a storage pool by aggregating remote drbd
> volumes into a VG and then any client can write to LV created in the VG.
> This solution can remove the limitation of single host's storage
> capacity when thin provisioning is enabled. 
> If thin-provisioning is enabled with drbdmanage, the new-added storage
> servers can't help the node which runs out of storage space.  
> That's why I care about the case of multiple primaries. Thanks for any
> feedback!

Fencing prevents split-brains in the first place, use it.

As for auto-recovery in dual-primary;

Consider that DRBD is not aware of data structures. So there is no safe
way to say how to merge data back. It would have to be done at the
FS-layer. If you simply said "well, sync over the node with older data",
or "sync over the node with fewer changes", consider this scenario; Your
accounting data is updated on one node, then sometime later, an ISO
image is written to the other node. I am pretty sure that the older,
smaller changes are a lot more valuable.

Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
access to education?

More information about the drbd-user mailing list