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

Arnold Krille arnold at arnoldarts.de
Mon May 21 20:41:41 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 Monday 21 May 2012 14:06:22 Florian Haas wrote:
> You've already stated that you're able to separate file access per
> node. And you only want access from two nodes, otherwise you wouldn't
> be considering DRBD. So, that makes your system a textbook use case
> for two separate single-Primary DRBD resources. This type of setup is
> orders of magnitude simpler to get right than a dual-Primary
> configuration, as both Arnold and Madison (digimer) have pointed out
> earlier. It completely sidesteps the issue of managing a cluster
> filesystem, and if you're concerned about being able to grow your
> filesystem later, just slap your DRBD resources onto LVM logical
> volumes, and you can resize at will (to the extent that your
> filesystem supports it).

The only down-side of "one single-primary-drbd per vm" is that you 'loose' 
live-migration compared to dual-primary or a cluster fs like gluster, moosefs, 
ceph or sheepdog.
Maybe one could try dual-primary-drbd as a direct image for a vm? But then 
dealing with split-brains (and their automatic resolve) and cluster-management 
is more complicated then just setting up one of the aforementioned distributed 
storage systems.

Have fun,

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