[DRBD-user] Adding an additional node to a 2-node DRBD cluster

[Luke Camilleri]

Hi Everyone, new to this list so any help would be greatly appreciated. Just installed DRBD and set it up on 2-nodes. I have then introduced a 3rd node to the cluster and it was to say the least cumbersome. The steps that I have followed were the below:

#drbdadm down drbd-2 (this has been run on all nodes)

I then followed the DRBD user guide 9.7.8 Changing the meta-data which suggest to run -max-peers=<N>

#drbdadm create-md drbd-2 --max-peers=3

Move internal meta data from last-known position?

[need to type 'yes' to confirm] yes

md_offset 10842271744
al_offset 0
bm_offset 0

Found ext3 filesystem
     9437184 kB data area apparently used
           0 kB left usable by current configuration

Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
   * use external meta data (recommended)
   * shrink that filesystem first
   * zero out the device (destroy the filesystem)
Operation refused.

So I increased the LV and the same output was received and then reduced the ext3 filesystem with resize2fs but still same output.

Bottom line, to have it working I had to:

# drbdadm wipe-md drbd-2

Do you really want to wipe out the DRBD meta data?
[need to type 'yes' to confirm] yes

Wiping meta data...
DRBD meta data block successfully wiped out.
# drbdadm create-md drbd-2 --max-peers=3
md_offset 10842271744
al_offset 10842238976
bm_offset 10841243648

Found ext3 filesystem
     9437184 kB data area apparently used
    10587152 kB left usable by current configuration

Even though it looks like this would place the new meta data into
unused space, you still need to confirm, as this is only a guess.

Do you want to proceed?
[need to type 'yes' to confirm] yes

initializing activity log
initializing bitmap (972 KB) to all zero
Writing meta data...
New drbd meta data block successfully created.
success

Afterwards I deleted the metadata on the secondary nodes and recreated it, and after a full-sync the files were synced from the primary. Finally my question is, is this the correct procedure or maybe there is a better way to achieve the introduction of new nodes in the DRBD cluster?

Systems details:
CentOS Linux release 7.6.1810 (Core)

kmod-drbd90-9.0.16-1.el7_6.elrepo.x86_64
drbd90-utils-9.6.0-1.el7.elrepo.x86_64

Thanks in advance for any feedback
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