A first look at shared virtual disks in Windows Server 2016

Posted on December 30, 2015 by workinghardinit

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:

No host level backup
No on line dynamic resize
No storage live migration
No checkpoints
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!

Creating a bootable VHD or VHDX from an existing one

Posted on December 2, 2015 by workinghardinit

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.

Recover From Expanding VHD or VDHX Files On VMs With Checkpoints

Posted on October 1, 2015 by workinghardinit

So you’ve expanded the virtual disk (VHD/VHDX) of a virtual machine that has checkpoints (or snapshots as they used to be called) on it. Did you forget about them? Did you really leave them lingering around for that long? Bad practice and not supported (we don’t have production snapshots yet, that’s for Windows Server 2016). Anyway your virtual machine won’t boot. Depending on the importance of that VM you might be chewed out big time or ridiculed. But what if you don’t have a restore that works? Suddenly it’s might have become a resume generating event.

All does not have to be lost. Their might be hope if you didn’t panic and made even more bad decisions. Please, if you’re unsure what to do, call an expert, a real one, or at least some one who knows real experts. It also helps if you have spare disk space, the fast sort if possible and a Hyper-V node where you can work without risk. We’ll walk you through the scenarios for both a VHDX and a VHD.

How did you get into this pickle?

If you go to the Edit Virtual Hard Disk Wizard via the VM settings it won’t allow for that if the VM has checkpoints, whether the VM is online or not.

VHDs cannot be expanded on line. If the VM had checkpoints it must have been shut down when you expanded the VHD. If you went to the Edit Disk tool in Hyper-V Manager directly to open up the disk you don’t get a warning. It’s treated as a virtual disk that’s not in use. Same deal if you do it in PowerShell

Resize-VHD -Path “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd” -SizeBytes 15GB

That just works.

VHDXs can be expanded on online if they’re attached to a vSCSI controller. But if the VM has checkpoints it will not allow for expanding.

So yes, you deliberately shut it down to be able to do it with the the Edit Disk tool in Hyper-V Manager. I know, the warning message was not specific enough but consider this. The Edit disk tool when launched directly has no idea of what the disk you’re opening is used for, only if it’s online / locked.

Anyway the result is the same for the VM whether it was a VHD or a VHDX. An error when you start it up.

[Window Title]
Hyper-V Manager

[Main Instruction]
An error occurred while attempting to start the selected virtual machine(s).

[Content]
‘DidierTest06’ failed to start.

Synthetic SCSI Controller (Instance ID 92ABA591-75A7-47B3-A078-050E757B769A): Failed to Power on with Error ‘The chain of virtual hard disks is corrupted. There is a mismatch in the virtual sizes of the parent virtual hard disk and differencing disk.’.

Virtual disk ‘C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD_8DFF476F-7A41-4E4D-B41F-C639478E3537.avhd’ failed to open because a problem occurred when attempting to open a virtual disk in the differencing chain, ‘C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd’: ‘The size of the virtual hard disk is not valid.’.

You might want to delete the checkpoint but the merge will only succeed for the virtual disk that have not been expanded. You actually don’t need to do this now, it’s better if you don’t, it saves you some stress and extra work. You could remove the expanded virtual disks from the VM. It will boot but in many cased the missing data on those disks are very bad news. But al least you’ve proven the root cause of your problems.

If you inspect the AVVHD/AVHDX file you’ll get an error that states

The differencing virtual disk chain is broken. Please reconnect the child to the correct parent virtual hard disk.

However attempting to do so will fail in this case.

Failed to set new parent for the virtual disk.

The Hyper-V Virtual Machine Management service encountered an unexpected error: The chain of virtual hard disks is corrupted. There is a mismatch in the virtual sizes of the parent virtual hard disk and differencing disk. (0xC03A0017).

Is there a fix?

Let’s say you don’t have a backup (shame on you). So now what? Make copies of the VHDX/AVHDX or VHD/AVHD and save guard those. You can also work on copies or on the original files.I’ll just the originals as this blog post is already way too long. If you. Note that some extra disk space and speed come in very handy now. You might even copy them of to a lab server. Takes more time but at least you’re not working on a production host than.

Working on the original virtual disk files (VHD/AVHD and / or VHDX/AVHDX)

If you know the original size of the VHDX before you expanded it you can shrink it to exactly that. If you don’t there’s PowerShell to the rescue if you want to find out the minimum size.

But even better you can shrink it to it’s minimum size, it’s a parameter!

Resize-VHD -Path “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd” -ToMinimumSize

Now you not home yet. If you restart the VM right now it will fail … with the following error:

‘DidierTest06’ failed to start. (Virtual machine ID 7A54E4DB-7CCB-42A6-8917-50A05354634F)

‘DidierTest06’ Synthetic SCSI Controller (Instance ID 92ABA591-75A7-47B3-A078-050E757B769A): Failed to Power on with Error ‘The chain of virtual hard disks is corrupted. There is a mismatch in the identifiers of the parent virtual hard disk and differencing disk.’ (0xC03A000E). (Virtual machine ID 7A54E4DB-7CCB-42A6-8917-50A05354634F)

What you need to do is reconnect the AVHDX to it’s parent and choose to ignore the ID mismatch. You can do this via Edit Disk in Hyper-V Manager of in PowerShell. For more information on manually merging & repairing checkpoints see my blogs on this subject here. In this post I’ll just show the screenshots as walk through.

Once that’s done you’re VHDX is good to go.

For a VHD you can’t shrink that with the inbox tools. There is however a free command line tool that can do that names VHDTool.exe. The original is hard to find on the web so here is the installer if you need it. You only need the executable, which is portable actually, don’t install this on a production server. It has a repair switch to deal with just this occurrence!

Here’s an example of my lab …

D:\SysAdmin>VhdTool.exe /repair “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD.vhd” “C:\ClusterStorage\Volume2\DidierTest06\Virtual Hard Disks\RuinFixedVHD_8DFF476F-7A41-4E4D-B41F-C639478E3537.avhd”

That’s it for the VHD …

You’re back in business! All that’s left to do is get rid of the checkpoints. So you delete them. If you wanted to apply them an get rid of the delta, you could have just removed the disks, re-added the VHD/VHDX and be done with it actually. But in most of these scenarios you want to keep the delta as you most probably didn’t even realize you still had checkpoints around. Zero data loss .

Conclusion

Save your self the stress, hassle and possibly expense of hiring an expert. How? Please do not expand a VHD or VHDX of a virtual machine that has checkpoints. It will cause boot issues with the expanded virtual disk or disks! You will be in a stressful, painful pickle where you might not get out of if you make the wrong decisions and choices!

As a closing note, you must have have backups and restores that you have tested. Do not rely on your smarts and creativity or that others, let alone luck. Luck runs out. Otions run out. Even for the best and luckiest of us. VEEAM has save my proverbial behind a few times already.

Lightning Fast Fixed VHDX File Creation Speed With ReFS on Windows Server 2016

Posted on August 27, 2015 by workinghardinit

In this blog post we’re going to take a quick look at the lightning fast fixed VHDX file creation speed with ReFS on Windows Server 2016. We’ll compare it to creating fixed VHDX files On NTFS with a SAN that supports ODX. Both the NTFS and the CSV volume are CSV disk in a Hyper-V cluster and the test is run on the same node. The ODX cabale SAN is a Dell Compellent with Storage Center 6.5.20.

We create on a selection of fixed VHDX files sizes (50GB, 100GB, 500GB and 1TB) on NTFS volume Windows Server 2016 host You can see the quite excellent results in file creation speeds with ODX.

These results are very good (DELL Compellent always did a great job implementing ODX) and the time to create a 1TB fixed VHDX is just over 5 seconds consistently. Impressive by any standard I would say! When we start using CSVs we can see that times double for the larger VHDX sizes but still +/- 12seconds for a 1TB disk is impressive by any standard. There is little difference whether the node where the script runs owns the CSV or not.

Can things be more impressive? Let’s do the same exercise on a ReFS volume on a Windows Server 2016 host. Same server, same SAN with ODX enabled but note that ReFS does not even support ODX, so it cannot be leveraged.

No matter what the file size of our fixed VHDX files they are created in just over 1 second consistently. This is very impressive.

When we use a CVS LUN we still see the same impressive results. On CSV LUNS not owned by the node where we execute the test script we see a creation time of 2 seconds for VHDX sizes of 1TB. Still lightning fast.

If you do not have a SAN that supports ODX you can see why ReFS might become a very attractive choice for the file system for your Hyper-V virtual machine data volumes in Windows Server 2016. I can see why they mentioned it as the preferred option for Storage Spaces Direct. Do note that ReFS does not support deduplication and/or UNMAP (I see no dedupe support yet for virtual server workloads on the horizon either yet?). If you move large amounts of data around ODX does provide significant assistance with this. So with ReFS go for a large SSD tier. Flash only without deduplication or erasure coding might be cost prohibitive I’m afraid.

But let this not put you off ReFS. It has many benefits in combination with storage spaces and these new VHDX operation capabilities just add to that. So for many environments with commodity based storage this has become an even more interesting choice.

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Category Archives: VHDX