I’m very excited to hear that coming in Windows Server 2019 there will be a few new features in regards to the File Share Witness for the Failover Cluster Quorum. The feature that many of my customers have been asking for about for many years is finally arriving…File Share Witness on a USB stick!
Okay, they didn’t really ask for that specifically, but many of my customers wanted to deploy a simple 2-node cluster in each store location, branch office, etc., and they didn’t want the added expense of a SAN to leverage a Disk Witness and weren’t to keen, or just didn’t have the connectivity, to rely on a Cloud Witness in Azure. Many of these customers just decided to forgo clustering, or they used an alternative clustering solution like the SIOS Protection Suite.
Now they have a viable alternative coming in Windows Server 2019. By leveraging a supported router, a USB disk inserted into the router can be configured with a file share that can be used as the witness. This eliminates the need for a 3rd server or internet connectivity.
There are a few scenarios I can imagine, from HCI for Hyper-V, to a simple file server cluster using DataKeeper. Regardless of the scenario, keep in mind unless you plan on building a workgroup cluster, you probably will want to run a VM on each server to act as a redundant Domain Controllers, unless you have a reliable WAN connection back to a Domain Controller hosted in your main datacenter.
I get asked this question all the time. People are concerned about losing their file share witness, so like many of their other shares, they want to leverage DFS for some additional availability. This is a very bad idea and is not supported.
Microsoft recently publish a great blog article that describes exactly why this is not supported.
Much of this article would also apply to people who ask if they can use a DataKeeper replicated volume resource as a Disk Share. It makes sense, you can use a DataKeeper volume resource in place of a Physical Disk resource for any other workload, so why not a Disk Witness?
This issue is the same as the DFS issue, in the event of a loss of communication between the two servers there is nothing to guarantee that the volume wouldn’t come online on both servers, causing a potential split-brain condition. The Physical Disk resource overcomes this issue by using SCSI reservations, ensuring the disk is only accessible by one cluster node at a time.
The good news is that Microsoft already blocks you from trying to us a replicated DataKeeper Volume resource and coming in Windows Server 2019 it looks like they will also block you from using a DFS share as a File Share Witness.
Really glad to hear today that I’ve been re-awarded the Microsoft Cloud and Datacenter Management MVP award for 2018. It’s a great honor to be counted among some of the smartest people I know. Looking forward to the launch of Windows 2019 and whatever else Microsoft have up their sleeves for Azure in 2019.