Set the preferred site for a CSV in a site-aware stretched failover cluster

Introduction

I have presented many time over the past tears on the new and enhanced capabilities of Microsoft Failover Clustering in Windows Server 2016 (Experts Live, Cloud & Datacenter Conference Germany, MicroWarehouse’s Windows Server 2016 Launch Event etc.) Feedback has shown me that there is still a lot of need for good failover cluster design and implementation guidance.

One area of enhancement is that you now have site-aware failover clusters in Windows Server 2016. That helps optimize the, availability, behavior and performance of the workload. It leveraged cluster fault domains and in this case those fault domains are the sites where the cluster nodes reside.

clip_image002

Set the preferred site for a CSV in a site-aware stretched failover cluster

You can leverage the site awareness to do all kind of configuration optimizations. You can set a preferred site creating a primary and a DRC site. The cluster behavior will optimize for that scenario. It will also help with situation like quorum split more easily and elegantly. You can create an “Active-Active” site configuration because a cluster groups, such as virtual machines can have their own preferred site.

As you can see in the picture above there is a thing called Storage Affinity. That means that VMs follow storage and are placed in same site where their associated storage resides. As such VMs will begin live migrating to the same site as their associated CSV after 1 minute. The CSV load balancer will distribute within the preferred site. That’s cool. But when setting a preferred site at the cluster group level like for virtual machines, how does one do this for a CSV?

It’s actually quite simple. A CSV is a cluster group, just like a VM is. So, for every CSV you can set that preferred site. You just grab the cluster group a bit differently. Let’s look at an example.

For a VM you’d do this: (Get-ClusterGroup -Name DidierTest01).PreferredSite = ‘Dublin’

Now for a CSV we go about it as follows:

Get-ClusterSharedVolume “Cluster Disk 1” | Get-ClusterGroup | Fl *

clip_image004

The preferred site has not been set yet. To set the preferred site for a CSV you can do the following:

$NTFS01 = Get-ClusterSharedVolume “Cluster Disk 1” | Get-ClusterGroup $NTFS01.PreferredSite = “Dublin”
$NTFS01.PreferredSite

clip_image005

You can remove a preferred site by setting it to $Null:

$NTFS01.PreferredSite = $Null

That was not to hard was it? There is one other thing to keep in mind. Do not forget to set up your site fault domains first and set the site for your cluster nodes before you start configuring preferred sites at the cluster group level or it will throw an error. That’s the minimal setup of a site-aware cluster you need to have in place before you can do more fine-grained configurations.

New-ClusterFaultDomain –Name Dublin –Type Site –Description “Primary” –Location “Dublin DC1”
New-ClusterFaultDomain –Name Cork –Type Site –Description “Secondary” –Location “Cork DC2″
Set-ClusterFaultDomain –Name Node-A –Parent Dublin
Set-ClusterFaultDomain –Name Node-B –Parent Dublin
Set-ClusterFaultDomain –Name Node-C –Parent Cork
Set-ClusterFaultDomain –Name Node-D –Parent Cork

 

If you don’t do this and try to set preferred sites at the cluster group level you’ll get an error like:

Exception setting “PreferredSite”: “Unable to save property changes for ‘e95ad724-97d3-4848-91db-198ab8312737’.
The parameter is incorrect”
At line:1 char:1
+ $NTFS01.PreferredSite = “Dublin”
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], SetValueInvocationException
+ FullyQualifiedErrorId : ExceptionWhenSetting

 

There is a lot more to say about site-aware stretched clusters but how to deal with setting a preferred site for a CSV must be the most common question I get on this subject. Well, now it’s published to help you all out. I hope it helps.

Cluster Shared Volumes without Active Directory

Introduction

Cluster Shared Volumes without Active Directory will come online if certain conditions are met. Basically, when the cluster can form. That’s what we’ll talk about here. There are a lot of things to consider when virtualizing your Active Directory environment, partially or completely. Too much for this blog post alone and much of it has been discussed before. Here I’ll discuss when people count on their Cluster Shared Volumes coming online when active directory is not available but are disappointed and think that it’s a bug or a broken promise. It is not! We know that since Windows Server 2012 the CSVs coming online do not depend on Active Directory being available (thanks to the local CLIUSR account being used for cluster starts).

Cluster Shared Volumes without Active Directory

So, let’s address getting your Cluster Shared Volumes online when AD is not available. The things to realize is that not having Active Directory has been taken care off. The thing that still can go wrong is that the cluster doesn’t come on line properly and that means that the CSV LUNs won’t be online as those are cluster resource. Hyper-V can boot the VMs without the cluster being formed but as the VMs reside on a CSV and those are not available, that’s what’s causing the problem. That means that getting your cluster to come up is the real issue.

Getting your cluster to come up is the real issue.

If cluster shared volumes can come up without a domain controller / AD being available since Windows Server 2012 (Failover Clustering and Active Directory Integration) how is it that some many people still have issues with it? How do you make this work for you? You can use a disk witness to protect you in most cases. When you have a file share or cloud witness you can take some step to avoid running into this issue.

There is a great article on cluster behavior here: Failover Cluster Node Startup Order in Windows Server 2012 R2 (the same rules apply for Windows Server 2016). Read it and you’ll notice that the behavior differs depending on whether you have a witness defined and whether that witness is a witness disk or a file share or cloud witness. The disk witness has a copy of the cluster database and if available will help you out of any situation where the paxos on the disk witness (if it’s available) is more recent then the one on the cluster node as the node will download the cluster database info from the disk witness. But a file share or cloud witness don’t have a copy, so they have a small disadvantage under certain scenarios. CSV’s that won’t come up is when booting the nodes in the wrong order when using a file share or cloud witness is one of those scenarios but not having AD isn’t the root cause of this.

Some people will never notice this issue at all, especially not when they have disk witness, but when they do, it might be at a very inconvenient moment in time. Examples of where this situation can occur are a single cluster environment where the domain controllers are running on CSV and high available in that cluster that was shut down completely, the cluster has a file share witness and the nodes are started in the wrong order.

Making sure your CSVs come online = clustering being formed

Well for one make sure you are using Windows Server 2012 or higher for your cluster. That’s a given.

Beyond that you basically just need to know what to do in what scenario to get your cluster up and running so you won’t have issues with getting the CSV to come up. You just have to follow some rules of thumb and you’ll be fine. Also, there’s almost always a way to get out of pickle, just don’t panic. But also remember that you can make your live easier when you design your solutions with failure in mind and by knowing your options so you can act correctly. I my example I’ll be using Hyper-V cluster with CSVs but the same goes for SOFS, SQL Server clusters leveraging CSVs etc.

Planned down time

If you’re shutting down a complete cluster you have two options to make sure things go a smooth as possible.

Option 1 – A clean cluster shutdown by the book

  • Shut down the workload, i.e. the VMs.
  • Stop the cluster
  • Shutdown the Cluster nodes.
  • Boot the cluster nodes. You can start with any you like. The CSVs will come on line. You will be able to start the VMs. Do start with the domain controllers and wait for them to come on line before starting the others.

During this you’ll see some “collateral” events, errors, warnings due to Active Directory not being available. The cluster name has issues without Active Directory but that a management connection point, it doesn’t mean the cluster doesn’t work. Once Active Directory is available the cluster name will come on line automatically when the default failure policy restarts it. You can also manage the cluster via RDP or console by connection to “.” locally on that node or use the running node name. You can also try to bring cluster name on line manually when Active Directory is up and running.

Option 2 – A clean cluster shutdown as it happens most of the times in real life

Which is one a lot of people do to keep part of the work load running as long as possible.

  • Shut down the no critical workload, i.e. the VMs.
  • Pause a node so the critical workloads live migrate to other nodes
  • When the node is paused, shut down the node.
  • You rinse and repeat this until the last node is left with only the most critical VMs

clip_image002

  • Finally, you stop the workload on that last cluster node and shut it down as well.
  • Now comes the critical part: Remember what node you shut down last. You have to start that one first and you’ll see that your CSV will come on line. If you boot another node, you might panic as the CSV will not come on line.

Now I need to correct this a little bit. With a disk witness you are OK whatever node you boot. When the paxos numbers on the first node to boot and the disk witness are compared the most recent copy will be used. Either the local one on the node will be used directly or after it has been updated with the data form the disk witness. To make things simple for the ops team I always tell them to note the last node they shut down anyway no matter what type of witness they have. It’s good info to have.

With a file share or cloud witness the shutdown/startup order really comes into play. The reason this happens is that by shutting down node by node we end up with a one node cluster (last man standing).  When that’s shut down that’s the only node that knows about the last (potential) changes in the cluster as it holds a copy of the cluster database. Remember that a files hare or a cloud witness has no copy of the cluster database. That’s why the last node to be shut down has to come on line first when comparing the paxos numbers with the witness as that node can form a cluster. If the node that boots first does not hold the most recent paxos number it cannot download the cluster databases info from the file share or cloud witness. Such a node cannot form a cluster and bring the CSVs online. If the first node to boot was the last one to shut down, it can form a cluster and the CSVs will come on line. This is the big difference with option one where you shut down the entire cluster and then take the nodes of line.

You might not know or remember the order. If that’s the case you still have options like starting the cluster node with the -fixquorum option (net.exe start clussvc /forcequorum) at the risk of loosing some cluster changes that are not in the local cluster database.

No need to go to immediately backups, extract the domain controller VMs from SAN snapshots or mount a LUN to a different machine to extract the VM files for the DC or so. Don’t panic!

One or more failed nodes

Well as long as the cluster survives your domain controller VMs should fail over. Keep ‘m on separate node (anti-affinity), separate CSV LUNs, if possible separate clusters if all domain controller virtual machines are going to be running high available on a cluster node and that cluster is still functional after all. No issues here.

Total cluster failure

The cluster nodes all show due to a “global” BSOD or are turned off due to a power failure or a storage array crash. This is more the realm of bad dreams I know, it does happen. Often things will recover and you’ll be fine but you can do your part. The same rules apply, get the cluster to form and you’ll have your CSVs on line. In a bad case -fixquorum is your friend but normally it’s not your first option. In the worst case you’ll need recovery from backup of the cluster or rebuild it. It’s a very bad day if it comes to that. And cluster recovery is not the subject of this post.

Conclusion

Don’t blame Active Directory and start troubleshooting or fixing the wrong problem. So yes, CSV will come on line when certain conditions are met and you can work yourself out of a pickle if needed. But during a disaster that’s only extra work and stress you might not want to worry about if you can avoid it. It’s good to know how to resolve issues around CSVs not coming online when the shit hits the fan as even the best laid out plans tend to get side tracked by reality when disaster strikes.

If you cannot guarantee control over all the prerequisites and might not have the skills in please when needed, you might consider other options. Some of these are actually the best practices of the past when a CSV would indeed not come on line without active directory in any way. This is great for AD related issues but not for you offline CSVs, they need the cluster to form properly!

Sure, you can run the domain controller virtual machines on local storage, and not made high available. This cloud be on one of the cluster nodes (*) or on a stand-alone Hyper-V host. Having a physical domain controller is also a possibility. This helps avoid issues with AD in virtualized environments as many other services are very dependent on them and it’s good to have on one available all of the time and get them back on line a.s.a.p..

I’ll leave you with the fact that virtualizing domain controllers can be done but it pays to study up on how to do it well and test your assumptions in the lab. There is a lot of information on virtualizing domain controllers for a reason. Read it and process what you’ve learned from it. You might find that this CCV thingies is not the most complex subject to deal with.

(*) Please note that some cluster deployments like HCI based on S2D do not support running other (local) storage in addition to the boot OS and the S2D storage pool volumes.

New SMB Instances in Windows Server 2016

Introduction

I’m pretty sure you all know / remember that in Windows Server 2012 R2 one of the improvements we got for SMB 3 was the default and the CSV instance. You can take a peak here at my slide deck from a presentation I gave at the Microsoft Technical Summit in Berlin 2014 Failover Clustering- What’s new in Windows Server 2012 R2

image

You can also read more on TechNet here.

We have New SMB Instances in Windows Server 2016

I’m happy to see this concept being expanded in the new SMB workloads. When playing  with Windows Server 2016 TPv5 I you’ll notice that we now have gotten extra SMB instances:

image

So what are these New SMB Instances in Windows Server 2016 about?

Default: This is what we had before, it’s nonspecific default SMB traffic, such as file shares

CSV: Also already known since Windows Server 2012 R2. This is the CSV traffic. This got isolated for better resiliency and isolation of issues. The goal was not to let CSV SMB issues affect default SMB traffic.

SR: This stands for Storage Replica. The purpose of this instance is the same as for CSV, isolate and make SMB on the whole more resilient.

SBL: This stands for “Storage Bus Layer”, which is related to Storage Spaces Direct replication traffic. The Storage Bus Layer is now called the Software Storage Bus (SSB). Again, isolated in its own instance for better resilience and isolation of issues. You can find more on the Software Storage Bus in Storage Spaces Direct and its use of SMB here Storage Spaces Direct – Under the hood with the Software Storage Bus

Picture by Microsoft®

“SSB uses SMB3 and SMB Direct as the transport for communication between the servers in the cluster. SSB uses a separate named instance of SMB in each server, which separates it from other consumers of SMB, such as CSVFS, to provide additional resiliency. Using SMB3 enables SSB to take advantage of the innovation we have done in SMB3, including SMB Multichannel and SMB Direct. SMB Multichannel can aggregate bandwidth across multiple network interfaces for higher throughput and provide resiliency to a failed network interface. SMB Direct enables use of RDMA enabled network adapters, including iWARP and RoCE, which can dramatically lower the CPU overhead of doing IO over the network and reduce the latency to disk devices”

Funny anecdote: while doing some research I stumbled upon the MSDN article MSFT_SmbShare class. As you can see in the screenshot below the name was mistakenly put at “Storage Bus Later” but it should be Storage Bus Layer or as it’s now called the Software Storage Bus:

clip_image002

Now that will be fixed soon or by the time you read this blog post. All fun aside, if you want to see what that Software Storage Bus is capable off look at this blog post and video by Ned Pyle on what Claus Joergenson achieved already in 2015 with this technology. Amazing results!

Defragmenting your CSV Windows 2012 R2 Style with Raxco Perfect Disk 13 SP2

When it comes to defragmenting CSV it seemed we took a step back when it comes to support from 3rd party vendors. While Windows provides for a great toolset to defragment a CSV it seemed to have disappeared form 3r party vendor software. Even from the really good Raxco Perfect disk. They did have support for this with Windows 2008 R2 and I even mentioned that in a blog.

If you need information on how to defragment a CSV in Windows 2012 R2, look no further.There is an absolutely fantastic blog post on the subject How to Run ChkDsk and Defrag on Cluster Shared Volumes in Windows Server 2012 R2, by Subhasish Bhattacharya one of the program managers in the Clustering and High Availability product group. He’s a great guy to talk shop to by the way if you ever get the opportunity to do so. One bizarre thing is that this must be the only place where PowerShell (Repair-ClusterSharedVolume cmdlet) is depreciated in lieu of chkdsk.

3rd party wise the release of Raxco Perfect Disk 13 SP2 brought back support for defragmenting CSV.

image

I don’t know why it took them so long but the support is here now. It looks like they struggled to get the CSVFS (the way CSV are now done since Windows Server 2012) supported. Whilst add it, they threw in support for ReFS by the way. This is the first time I’ve ever seen this. Any way it’s here and that’s good because I have a hard time accepting that any product (whatever it does) supports Hyper-V if it can’t handle CSV, not if you want to be taken seriously anyway. No CSV support equals = do not buy list in my book.

Here’s a screenshot of Perfect disk defragmenting away. One of the CSV LUNs in my lab is a SSD and the other a HDD.

image

Notice that in Global Settings you can tweak the behavior when defragmenting optimization of various drive types, including CSVFS but you just have to leave the default on unless you like manual labor or love PowerShell that much you can’t forgo any opportunity to use it Winking smile

image

Perfect disk cannot detect what kind of disks you have behind the CSV LUN so you might want to change the optimization method if you’re running SSD instead of HHD.

image

I’d love for Raxco to comment on this or point to some guidance.

What would also be beneficial to a lot of customers is guidance on defragmentation on the different auto-tiering storage arrays. That would make for a fine discussion I think.