Category: Words

As shown in my last post, I recently added some storage to our SAN, and will be moving existing VHD files from our Hyper-V cluster to this new storage.

The unique thing about this is that these VHD’s contain data that is being served with Microsoft DFS and replicated with DFSR. Hopefully word is spreading about DFSR data stores requirements for backup, which include some specific requirements for backup, especially when it comes to snapshots due to the multi-master database DFSR uses. Because of this information, I was a little concerned about the Quick Storage Migration (QSM) and so I started digging.

I eventually came across this blog post that went into detail about how the QSM works; It mentions that it does a snapshot of the VM and creates differencing disks, and eventually the snapshot is merged and VM restarted from that saved state. At this point I was concerned about my DFS data and so I sent an email to the wonderful and always helpful AskDS blog seeking clarification.

 

Here’s the response from Ned Pyle:

My presumption is that this is safe because – from what I can glean – this feature never appears to roll back time to an earlier state as part of its differencing process.

He then went the extra mile and contacted internal Microsoft peers closely related to the QSM feature, who responded:

That’s correct, we don’t revert the machine state to an earlier time. A differencing disk is created to keep track of the changes while the parent vhd is being copied. Once the VHD is copied, the differencing disk is merged into the parent.

 

Based on that I performed a QSM of my 1.6 TB VHD yesterday. It took 12.5 hours to complete, but in the end it was fully successful, with no negative repercussions.

Something interesting to note, is that I had to manually move a different 350GB vhd file to my new storage first, instead of a QSM since I was out of space on the original storage to create the avhd differencing disk. I shut down the VM, transferred the VHD (took about an hour), and then re-pathed it within the VM settings and turned the VM back on.

Following this I received a DFSR error # 2212 that “The DFS Replication service has detected an unexpected shutdown on volume F:”. I’m not sure why this occurred, and I only did the one transfer so I can’t verify that it wasn’t related to some other operation or bad shutdown.

 

Thanks to Aidan Finn and this blog post, I’ve recently discovered that how I planned the licensing for my Hyper-V cluster is incorrect.

With two Dell R410’s in a Hyper-V cluster, I purchased two licenses of Windows Server 2008 R2 Enterprise. I figured that as long as I didn’t run more than 4 VMs per host, I’d be good. In the case of a Live Migration or fail over, the VMs weren’t permanently assigned to the other host so it’d be alright. For future VMs, one off purchases of Server Standard would be made to allow for their use.

I really don’t understand why Microsoft doesn’t make it more obvious that Datacenter really is what’s necessary to run a Hyper-V cluster. Unless you’re running 4 VM’s or less across two hosts, Datacenter is the only way to go. Any more than that, and you’ll be doubling up on Enterprise licenses for each host, which by that point you might as well buy Datacenter. For a two host Hyper-V cluster this will cost between $12,000-15,000.

I’m assuming this is just as much of a problem for ESXi clusters too; apply a Windows license to each host even though it isn’t running Windows, so that during failover, the licensing is legal.

 

At least now I know that this is incorrect, so for 2012 fiscal two Windows Server Datacenter licenses will be purchased. Of course with Windows 8 around the corner, I’ll be getting these licenses with Software Assurance (assuming Windows 8 isn’t out yet).

Thinking about Datacenter has got me really excited actually, because of the additional Hyper-V features, future improvements to DFS and DFSR (which I’m anxiously awaiting news of) and updated OS for WDS, RDS and a bunch of other services.