Category Archives: Hyper-V

A first look at shared virtual disks in Windows Server 2016

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Introduction

Time to take a first look at shared virtual disks in Windows Server 2016 and how they are set up. Shared VHDX was first introduced in Windows Server 2012 R2. It provides shared storage for use by virtual machines without having to “break through” the virtualization layer. This way is still available to us in Windows Server 2016. The benefit of this is that you will not be forced to upgrade your Windows Server 2012 R2 guest clusters when you move them to Windows Server 2016 Hyper-V cluster hosts.

The new way is based on a VHD Set. This is a vhds virtual hard disk file of 260 MB and a fixed or dynamically expanding avhdx which contains the actual data. This is the “backing storage file” in Microsoft speak. The vhds file is used to handle the coordination of actions on the shared disk between the guest cluster nodes?

Note that an avhdx is often associated with a differencing disk or checkpoints. But the “a” stands for “automatic”. This means the virtual disk file can be manipulated by the hypervisor and you shouldn’t really do anything with it. As a matter of fact, you can rename this off line avhdx file to vhdx, mount it and get to the data. Whether this virtual disk is fixed or dynamically expanding doesn’t matter.

You can create on in the GUI where it’s just a new option in the New Virtual Hard Disk Wizard.

Or via PowerShell in the way you’re used to with the only difference being that you specify vhds as the virtual disk extension.

In both cases both vhds and avhdx are created for you, you do not need to specify this.

You just add it to all nodes of the guest cluster by selecting a “Shared Drive” to add to a SCSI controller …

… browsing to the vhds , selecting it and applying the settings to the virtual machine. Do this for all guest cluster nodes

Naturally PowerShell is your friend, simple and efficient.

Rules & Restrictions

As before shared virtual disk files have to be attached to a vSCSI controller in the virtual machines that access it and it needs to be stored on a CSV. Both block level storage or a SMB 3 file share on a Scale Out File Server will do for this purpose. If you don’t store the shared VHDX or VHD Set on a CSV you’ll get an error.

Sure for lab purposes you can use an non high available SMB 3 share “simulating” a real SOFS share but that’s only good for your lab or laptop.

The virtual machines will see this shared VHDX as shared storage and as such it can be used as cluster storage. This is an awesome concept as it does away with iSCSI or virtual FC to the virtual machines in an attempt to get shared storage when SMB 3 via SOFS is not an option for some reason. Shared VHDX introduces operational ease as it avoids the complexities and drawbacks of not using virtual disks with iSCSI or vFC.

In Windows Server 2012 R2 we did miss some capabilities and features we have come to love and leverage with virtual hard disks in Hyper-V. The reason for this was the complexity involved in coordinating such storage actions across all the virtual machines accessing it. These virtual machines might be running on different hosts and, potentially the shared VHDX could reside on different CSVs. The big four limitations that proved to be show stopper for some use cases are in my personal order of importance:

  1. No host level backup
  2. No on line dynamic resize
  3. No storage live migration
  4. No checkpoints
  5. No Hyper-V Replica support

I’m happy to report most of these limitations have been taken care of in Windows Server 2016. We can do host level backups. We can online resize a shared VHDX and we have support for Hyper-V replica.

Currently in 2016 TPv4 storage live migration and checkpoints (both production and standard checkpoints) are still missing in action but who knows what Microsoft is working on or has planned. To the best of my knowledge they have a pretty good understanding of what’s needed, what should have priority and what needs to be planned in. We’ll see.

Other good news is that shared VHDX works with the new storage resiliency feature in Windows Server 2016. See Virtual Machine Storage Resiliency in Windows Server 2016 for more information. Due to the nature of clustering when a virtual machine loses access to a shared VHDX the workload (role) will move to another guest cluster node that still has access to the shared VHDX. Naturally if the cause of the storage outage is host cluster wide (the storage fabric or storage array is toast) this will not help, but other than that it provides for a good experience. The virtual machine guest cluster node that has lost storage doesn’t go into critical pause but keeps polling to see if it regains access to the shared VHDX. When it does it’s reattached and that VM becomes a happy fully functional node again.

It also supports the new Storage Qos Policies in Windows Server 2016, which is something I’ve found during testing.

Thanks for reading!

Accelerated Checkpoint merging with ReFS v2 in Windows Server 2016

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Introduction

This blog post is a teaser where we show you some of the results we have seen with ReFS v2 in Windows 2016 (TPv4). In a previous blog post (Lightning Fast Fixed VHDX File Creation Speed With ReFS on Windows Server 2016) we have demonstrated the very fast VHDX file creation capabilities we got with ReFS v2. Now we look at another benefit of ReFS v2 in a Hyper-V environment, thanks to a feature or ReFS v2 called block cloning. We get accelerated checkpoint merging with ReFs v2 in Windows 2016

The Demo

For this short demo we have a virtual machine running Windows Server 2016. It resides on a CSV formatted with REFS (64K unit allocation size). Inside the virtual machine there is a second data disk. Our  VM called CheckPointReFS (64K unit allocation size) has this data volume formatted with ReFS (64K unit allocation size) and it runs on the ReFS formatted CSV. The disks in this test are fixed sized VHDX files.

On the data volumes we have about 30GB worth of ISO files. We checkpoint the VMs and then create a copy of those files on the data volume.

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We then delete this checkpoint.

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Via the events 19070 (start of a background disk merge) and 19080 (completion of a background disk merge) in the Microsoft-Windows-Hyper-V-VMMS/Admin logs we calculate the time this took: 5 seconds.

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There are moments you just have to say “WAUW”. Really this rocks and it’s amazing. So amazing I figured I made a mistake and I ran it again … 4 seconds. WOEHOE!  What where the times you saw when you last deleted a large checkpoint?

I am really looking forward to do more testing with ReFS v2 capabilities with Hyper-V on Windows 2016.

Creating a bootable VHD or VHDX from an existing one

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Creating a bootable VHD or VHDX from an existing one is a great capability to have.There are a couple of reasons why one might need or want to do this. In windows 2012 (R2) this is even a part of normal live migration operations. Storage live migration for example is nothing but the live streaming of the data of your live virtual hard disk into a new VDH/VHDX. You have multiple options when it comes to creating a bootable VHD/VHDX from an existing one and they all serve their specific purposes,which might or might not overlap.

This is great stuff to do migrations, reorganize storage, defrag your internal dynamic VHDX structure etc.  But you’re not limited to those options. When you want to convert from VHD to VHDX you’ll leverage Convert-VHDX. You can also create a new VHDX with an old one as the source with New-VHDX. Great for all kind of operations including off line migration, updates, testing on exact copies of the original disk etc. You might think it’s better to just copy the disk but for a conversion that will not work, that won’t deal with internal fragmentation which can be important for performance testing when your migrating to new storage, a new cluster & Hyper-V version and such.

Recently people asked me if this would work with their OS disk. The virtual disk that the boot from. Yes that will work. Both New-VHD and Convert-VHD will create a fully bootable new virtual disk if the source virtual disk was bootable to begin with. No problem, They have to, if you think about it. Using Convert-VHD to move from VHD to VHDX and even change the cluster sizes of the disk would be no good if the VM doesn’t boot anymore. Like wise with New-VHD.

The only thing that need some real tender loving care is when you convert a VM from generation to generation 2. The script provided to to that by John Howard (MSFT) use fully supported technologies. The script itself is not a supported product, but you’re not doing anything unsupported with it.

So all people needing to convert, defrag or move  VMs to new virtual hard disks. Do a few test to verify your assumptions and go forward. Step into that bright new future you’ve been missing out on for the past 3 years.

Windows Server 2016 TPv4 Hyper-V brings virtual machine configuration version 7

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When building a Windows Server  2016 TPv4 Hyper-V cluster this weekend I noticed that we now have a new version of the virtual machine configuration.

When we migrate (rolling cluster upgrade, move to new cluster or host, import on new cluster or host) virtual machines to  Windows Server 2016 Hyper-V from Windows Server 2012 R2, the virtual machine’s configuration file isn’t automatically upgraded. In the past it was, which blocked moving back to a previous edition of Hyper-V. Now we can do this until we manually update the virtual machine configuration version.  This block going back but it enables our new virtual machine features. Version 5.0 is the one that’s compatible with Windows Server 2012 (R2) Windows Server 2016. Version 6.2 was what we had in TPv3 and could only run on Windows Server 2016. Windows Server 2016 TPv4 Hyper-V brings virtual machine configuration version 7.

When you have virtual machines that come from  Technical Preview v3 and you had updated the virtual machine configuration of your virtual machines or created brand new ones these would be at version 6.2. Since I do not consider it wise to keep testing these on a version of a previous preview I updated them all to version 7.

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The code below grabs all VMs on all cluster nodes (even the none clustered VMs), shuts them down, updates the configuration version and starts them again. It’s just a quick example.

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Now do NOT do this to virtual machines with configuration version 5 that you might want to move back / import to a Windows Server 2012 R2 Hyper-V host. But if you know you’ll be testing with the new features, have a blast, like me here on the TPv4 lab cluster.

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I’m still looking for the features version 7.0 enables, probably nested virtualization is one of those features I’m guessing. Happy testing!