DRBD lvm replication details

DRBD LVM replication details

The scenario: 

Customer is setting up DRBD chef server. They have 1 TB raid array, but only use around 2 GB of that
space for chef server. Our directions call out for setting up LVM at 80% of physical volume for bit 
level replication.

Customer wanted to know if we can setup LVM for a much smaller chunk of the RAID so they can utilize 
the rest of it for soemthing else, for example Nexus.

A: 

[8:29 AM] Steven Danna: @alex I think I gave you that answer under caffenated
		drbd does replicate at the block device level
		but I'm pretty sure that the block device we replicate is the one that lvm exposes 
		to us not the underlying disk
		@sh can you confirm that ^
		as in , drbd replicates /dev/opscode/drbd not the underlying disk itself.
		(the good/bad news is that just in time to help fix it all, my brain seems to be 
		shedding intimate knowledge of our HA stack).


[8:32 AM] Josh Glass: # resource pc0 on PRDSLSLAOPCHB01: not ignored, not stacked # defined at 
/var/opt/opscode/drbd/etc/pc0.res:1 resource pc0 { on PRDSLSLAOPCHB01 { device /dev/drbd0 minor 0; 
disk /dev/opscode/drbd; meta-disk internal; address ipv4 10.209.241.3:7788; } on PRDSLSLAOPCHF02 { 
device /dev/drbd0 minor 0; disk /dev/opscode/drbd; meta-disk internal; address ipv4 10.211.1.146:7788; }
disk { resync-rate 40M; } }
[8:32 AM] Steven Danna: yeah: disk /dev/opscode/drbd
[8:32 AM] Josh Glass: that's the lvm right?
[8:32 AM] Steven Danna: yeah
		Alex seems to disappear the moment after he comments, but hopefully he'll come back to see my error :\
[8:34 AM] Sean Horn: @ssd @glass So, we are agreeing that DRBD replicates only whatever LV it is configured with?
[8:34 AM] Steven Danna: correctus
[8:34 AM] Steven Danna: well, drbd doesn't care about "LVs" but the only block device we show it is the opscode/drbd lv
		no other lv's are replicated
[8:35 AM] Sean Horn: @ssd Yes, more accurately ^
[8:35 AM] Steven Danna: @alex for my sanity, drop me a line at some point to confirm you got the correction