Those test and demos were done with block lever storage, CSV on Fibre Channel, iSCSI or shared SAS. Today we’ll look at the experience when you’re running your VMs on a continually available file share on a Scale Out File Server (SOFS). This configuration offers the best possible experience.
Why well, when the cluster node is in Isolated mode this has no impact on the SOFS share as this is a resource external to the Hyper-V cluster. In other words it remains on line. This means that the VMs, even if they have lost their high availability during the time the node is Isolated, they keep running. After all there is nothing wrong with Hyper-V itself. With block level CSV storage you lose access to the storage as that a cluster resource and the node got isolated. That’s why the VMs go into a paused critical state during a transient failure with block level storage but they don’t when you’re using SOFS.
The virtual machine compute resiliency feature in action shows you that the VMs service a transient failure without issues. Your services need never know something was up. Even when the transient failure is reoccurring that doesn’t mean it will cause down time. The node will be quarantined and if it come backup the workload will be live migrated away.
You can watch a video of this in action here on Vimeo:
The quarantine threshold and duration as well as the resiliency period and can be tweaked to your environment to get the best possible results.
SMB 3 for the win! This is yet one more convincing argument to start looking into SOFS and leveraging the capabilities of SMB3. Remember that you can run as SOFS cluster against your existing shared storage to get started if you can get the IOPS/latency you require. But also look into storage spaces, especially storage spaces direct which avoids some of the drawback SANs have in such a scenario. High time for storage vendors to really scale out, implement SMB 3 well and complete and keep the great added value features they already have in their offering. It’s this or becoming yet a bit more irrelevant in todays storage scene in the Microsoft ecosystem.
Some enhancements only become truly evident to people when they see them in action. For many features this means something need to go wrong before they kick in. Others are more visible during normal operations. This is the case with the CSV enhancements in Windows Server 2012 R2 Failover Clustering.
One golden nugget here is the CSV placement policy (which really shines in combination with SOFS/Storage Spaces). This will spread ownership of the CSV amongst the cluster nodes to ensure a balanced distribution. In a failover cluster, one node is the “coordinator node” (owner) for a CSV. The coordinator node owns the physical disk resource that is associated with a logical unit (LUN). All I/O operations for the File System on that LUN are are through the coordinator node. In previous versions there is no automatic rebalancing of coordinator node assignment. This means that all LUNs could potentially be owned by the same node. In storage spaces & SOFS scenarios becomes even more important.
It helps all nodes carry their share of the workload as it load balances the disk I/O.
Failovers of CSV owners are potentially quicker and more predictable/consistent as an even distribution ensures that no one node owns a disproportionate number of CSVs.
When losing storage access the number of CSVs that are in redirected mode is potentially less as they are evenly distributed. In an unbalanced cluster it could be for all of them in a worse case scenario.
When using SOFS with Storage Spaces it makes sure the Storage Spaces Ownership is distributed fairly.
When does it happen
Each time a node leaves or joins the cluster. This means you don’t need to intervene manually or via PowerShell to get an even distribution. This goes for both exiting nodes as when adding a new node. The new node will get a CSV assigned if there is any on surplus on one of the existing nodes.
The process also works when you start a failover cluster when it has shut down.
When customers see this in action (it’s most obvious when then add a node as then they are normally watching) they generally smile as the cluster does it job getting the best possible results out of their hardware.
Everybody is very busy and I’m a bit tires but here’s the 6th episode of the Hyper-V Amigos show cast. In this episode we get to play a bit with storage spaces in Carsten’s lab.
As always we had a lot of fun doing so and thanks to Carsten Rachfahl and the assistance of Kerstin (his charming wife, also an MVP, in Office 365) we could simulate hardware failures & film them for you!
Carsten & I discuss several scenarios and what’s happening during failovers. Carsten is assisting customers with this a lot so he has some of the most varied experience with storage spaces and SOFS out there! Interesting stuff and for people who haven’t even looked at Windows Server 2012 or later yet a wake up call to start as the world is not limited to what we once knew. It’s not your daddy’s Windows anymore
I hope you enjoy it and we’re already planning for the next one!