[DRBD-user] Reasons not to use allow-two-primaries with DRDB

Arnold Krille arnold at arnoldarts.de
Sat May 19 19:54:12 CEST 2012

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


On Friday 18 May 2012 18:29:11 karel04 at gmail.com wrote:
> I am in the process of setting up DRBD on my servers, the network
> bandwidth being the bottleneck.  After having evaluated GlusterFS I
> realised, that I need the instant read access offered by DRBD.
> 
> Logically I am able to separate partitions that would require access
> from both nodes, and partitions where an asynchronous master-slave
> sync is sufficient.  But as far as I understand, the benefits from
> using Protocol A instead of C are limited, when the network is stable.
> 
> My question:
> Are there any additional benefits from NOT using two primaries or
> additional risks when using it? eg. would there be significant
> performance gain by using ext4 instead of GFS2/OCFS2? Anything else I
> should take into consideration?

A) There is a huge performance gain from using extX over gfs2/ocfs2, 
especially when you implement it wrong/incomplete as I did:-( Not doing 
fencing is basically killing gfs2 and ocfs2. Which I didn't want to do for a 
variety of reasons.
B) There is a huge latency improvement when using protocol A or B over C. The 
docs say that you loose reliability unless the second machine (and the 
switches in between) have battery backup. Which they should have unless you 
use one UPS for everything.
C) There is a huge administration gain when using "simple" single-primary and 
traditional fs.

My two cents...

Have fun,

Arnold
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