[DRBD-user] (newbie question) DRBD 9, pure controller without data storage

Roland Kammerer roland.kammerer at linbit.com
Tue Dec 5 10:16:49 CET 2017

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

On Mon, Dec 04, 2017 at 11:10:16PM +0000, Riches Jr, Robert M wrote:
> (This is a newbie question.)
> Having got non-LVM version 9 drbdadm working with two storage nodes and a
> few no-local-storage nodes, I'm attempting to graduate to using drbdmanage
> and LVM.  My goal is to have two storage nodes, one pure controller node
> without data storage, and a few no-local-storage compute nodes.  However, I
> don't understand the green box in Figure 5 in the User's Guide, labeled as a
> 'Control node', 'controlvolume is a local LV', 'pure Controller', and 'nodes
> without data storage'.  This is the figure:
> https://docs.linbit.com/ug-src/users-guide-9.0/images/drbdmanage-venn.png
> The only LVM volume group I see mentioned in chapter 5 of the DRBD 9 UG
> is the one it suggests to name 'drbdpool'.  However, if the pure controller
> has no data storage, how can the controlvolume be a local LV.  Can someone
> please enlighten a newbie on what seem to be contradictory descriptions?

There are two types of storage drbdmange can use:
- the control volume (which is the cluster wide database, 2x4MB, always
  on thick LVM)
- the storage for your actual DRBD resources (LVM/ZFS thin/thick).

That makes 4 combinations:
- The node has a copy of the control volume, that makes it a "control
  node". It can then provide storage for DRBD resources or not (control
  node or pure controller). A use case for a pure controller might be a
  "quorum node" that just has a copy of the cluster DB. Let's say you
  have 3 nodes, one of them is a pure controller, one of the other nodes
  fails then the cluster can continue as it still has 2 nodes with a
  copy of the control volume.
- The node does not have a copy of the cluster DB and gets its cluster
  DB from another node via TCP. These are satellites. They can have
  local storage for DRBD resources or not.

Regards, rck

More information about the drbd-user mailing list