[DRBD-user] Re: Suggestion to prevent split brain situation

Florian Haas florian.haas at linbit.com
Wed Dec 5 09:09:49 CET 2007

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

On Wednesday 05 December 2007 01:37:00 Kelly Byrd wrote:
> > And is it correct that DRBD only supports a single IP per machine using
> > the "address" directive? In that case the redundant link is only useful
> > for HeartBeat, but not to DRBD?
> Use the bonded driver. Depending on the bond mode, you can get just
> redundancy or you get increased bandwidth and redundancy.

Correct, but

- increased bandwidth isn't worth much for improving DRBD performance unless 
your disk I/O subsystem can indeed write faster than 110 MB/s (unlikely in 
the case of Bas' servers I suppose);
- added redundancy doesn't make a huge difference in case you are using 
crossover cables between nodes (which, when they fail due to hardware issues, 
typically don't fail in a way that the bonding driver would detect). 

If and when you're running DRBD replication over switches, you had better make 
sure that your cables are routed through physically separate switches hooked 
to independent power sources. Otherwise, again, bonding doesn't do you any 
good either. 

Our recommendation thus is generally to use a passive (i.e. back-to-back) 
network connection for your DRBD replication. Crossover cable is highly 
likely to provide the best MTBF. Add Heartbeat with that connection and a 
separate one via your switched LAN, plus dopd, and you're good to go.

Just my €.02.


: Florian G. Haas
: LINBIT Information Technologies GmbH
: Vivenotgasse 48, A-1120 Vienna, Austria

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