DRBD

DRBD handles the disk stuff. It's kinda like raid1 but over a network.

Sometimes the nodes may refuse to connect. If this happens, check 'dmesg' for the message drbd1: Split-Brain detected, dropping connection! This means that at some point, both of them thought they were primary. This can cause possible FS corruption, so drbd says that a human has to do something about it. The best thing to do is to run drbdadm invalidate on the host that doesn't have the data you want (usually the backup one). You will then be able to re-connect the nodes, and they will resync.

If the drbd connection is on the same link that the heartbeat is, you will always have a split-brain when the network cable is pulled. This is why we have automatic split-brain recovery enabled- the one that was most recently primary is the one that is considered authoritative. You can specify this with net { after-sb-0pri discard-older-primary; after-sb-1pri consensus; }

in drbd.conf

After you change a config file, you can update the node with drbdadm adjust You can then check to see if it worked (or to see other options if you're curious) with drbdsetup /dev/drbd# show

Here are my preferred network options: net { after-sb-0pri discard-older-primary; after-sb-1pri consensus; always-asbp; timeout 30; connect-int 5; ping-int 5; } Jdhutchin@ugcs.caltech.edu 22:08, 7 June 2008 (PDT)

Initial Setup
After you configure the resource in /etc/drbd.conf, you have initialize it and bring it up on both nodes with drbdadm create-md drbdadm up

You will then have to pick one node to be the first primary (if it's a resource from existing data, you should obviously pick that one, otherwise it doesn't matter) and then start the first sync by running drbdadm -- --overwrite-data-of-peer primary