[DRBD-user] two primaries, writes when disconnected - will it always be a split-brain?

Tomasz Chmielewski mangoo at wpkg.org
Fri Jan 25 18:25:20 CET 2008

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

I want to have two DRBD primaries.

On top of DRBD there will be a LVM.

LVM will consist of many logical volumes, and:
- the same logical volume will never be accessed concurrently by both 
DRBD machines,
- there will be no LVM metadata changes

In other words, this is a DRBD device (let's suppose a "D" as a small 
part of a DRBD device):


The first machine will only write to areas on DRBD device marked by "1":


The second machine will only write to areas on DRBD device marked by "2":


What will happen after a longer disconnection (say, one day, both 
machines do lots of writes, but never to the same place)?

Will they sync properly, and everything will play well?

Or perhaps it will be a split-brain, as LVM block size does not match 
DRBD block size, they may overlap, and the things will break?

Tomasz Chmielewski

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