[DRBD-user] Understanding "classic" 3 node set up.

[Paul O'Rorke]

Hi

I hope this is the right place to ask what may be a silly question.  I 
have searched the archives and still do not understand properly how to 
set up "classic 3 node" for DR.

I have been using a simple HA setup for some years now for KVM virtual 
machines.  I have a DRBD resource for each VM, backed by LVM volumes, 
each using a unique IP (aliases) via CAT5 directly connecting dedicated 
NICs on each of "alice" and "bob" (I'm using the example from the docs 
here for simplicity).  I run half the guests on each host and manually 
fail over if it is ever needed. This has been rock solid for me, great 
performance and has on more than one occasion saved my bacon.  I want to 
set up a classic 3 node DR with a VPN connected off site 3rd stacked node.

Referring to this 
http://docs.linbit.com/docs/users-guide-8.4/#s-three-nodes 6.18.2. 
Configuring a stacked resource

I don't understand where to set up the interface for the stacked resource:

|stacked-on-top-of r0 { device /dev/drbd10; address 192.168.42.1:7788; }|

What interface gets this IP?  I am assuming it goes on the primary node 
of the lower resource.  So for the example in the docs, if alice is the 
primary I set up 192.168.42.1:7789 on alice and if I have to switch bob 
to primary I loose replication to charlie until such time as I either 
restore alice as the primary or can I set up 192.168.42.1:7789 on bob 
somehow and continue off site replication while alice is down?

As I am reading it bob has no "knowledge" of charlie and the upper 
resource can only function while alice is primary.  Is that right?

Sorry if this is explained somewhere and I missed it.

regards

-- 

*Paul O'Rorke*
*Tracker Software Products (Canada) Limited *
www.tracker-software.com <http://www.tracker-software.com/>
Tel: +1 (250) 324 1621
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