EnableResignature and/or DisallowSnapshotLUN

http://www.yellow-bricks.com posted this blog post titled : EnableResignature and/or DisallowSnapshotLUN Full Blog Post ( site : http://www.yellow-bricks.com/2008/12/11/enableresignature-andor-disallowsnapshotlun/ )

I’ve spend a lot of time in the past trying to understand the settings for EnableResignature and DisallowSnapshotLUN. It had me confused and dazzled a couple of times. Every now and then I still seem to have trouble to actually understand these settings, after a quick scan through the VCDX Enterprise Study Guide by Peter I decided to write this post and I took the time to get to the bottom of it. I needed this settled once and for all, especially now I start to focus more on BC/DR.

According to the San Config Guide(vi3_35_25_san_cfg.pdf) there are three states:

  1. EnableResignature=0, DisallowSnapshotLUN=1 (default)
    In this state, you cannot bring snapshots or replicas of VMFS volumes by the array into the ESX Server host regardless of whether or not the ESX Server has access to the original LUN. LUNs formatted with VMFS must have the same ID for each ESX Server host.
  2. EnableResignature=1, (DisallowSnapshotLUN is not relevant)
    In this state, you can safely bring snapshots or replicas of VMFS volumes into the same servers as the original and they are automatically resignatured.
  3. EnableResignature=0, DisallowSnapshotLUN=0 (This is similar to ESX Server 2.x behavior.)
    In this state, the ESX Server assumes that it sees only one replica or snapshot of a given LUN and never tries to resignature. This is ideal in a DR scenario where you are bringing a replica of a LUN to a new cluster of ESX Servers, possibly on another site that does not have access to the source LUN. In such a case, the ESX Server uses the replica as if it is the original.

Please read the full post on this, as it is a complicated topic.
I ran in to this, when I was unplugged and replugging in multiple sata drives into different ports on my unsupported ESXi box. The test box would see the drive but not the datatstore, therefore I had to enable Resignature to get it to see it again.

Thanks to Duncan for this.