How to compact VHDX files in the most efficient way

C:Amie/ / Hyper-V, Microsoft, Storage

Have you ever run the Hyper-V “Edit Disk…” tool’s ‘compact’ action, to discover that your VHD or VHDX disk file didn’t shrink? This article discusses how to optimise the chances for success when compacting your virtual hard drives on Windows Server.

 

Why Compact VHDX files?

Compacting virtual disk files is an activity that most Hyper-V administrators seldom ever do. In most cases, the space savings are going to be nominal and outweigh the benefits. A well designed Hyper-V deployment will ensure accounting for future storage optimisation/loading during the capacity planning phase; with scale-out design considerations being made during this stage too.

Compaction is not a fix for poor design.

If you are unfamiliar with what compaction does at the technical level, Alataro has a good introduction guide.

View: Altaro “Why You Should Be Compacting Your Hyper-V Virtual Disks”

In practice, compaction can help in two scenarios:

  1. Improving the speed and disk space use for non-VSS block-based backups
  2. Reducing the amount of data transferred during live migration

 

Why doesn’t Edit Disk… work?

It is common for the Hyper-V Manager Compact tool to not achieve any reduction in the size of the VHDX file, putting many administrators off from spending time running it.

Two problems exist with the GUI compaction wizard:

  1. The VHDX file is not in a pre-optimised state prior to compaction, reducing the success rate
  2. For performance reasons. Execution through the wizard does not use the full range of compaction tools available to the system. These can only be accessed (currently) via PowerShell.

So how do you properly shrink a virtual disk?

 

Optimise your VM

Inevitably there will be some data inside the VM which is not necessary to retain. Removing this prior to compaction, will automatically increase the amount of space that you save.

Optimising Windows

Under Windows, running the Disk Clean-up tool is a good place to start. Additional places to clear-out include:

  1. C:\Windows\Temp
  2. C:\Windows\SoftwareDistribution\Download
    The SoftwareDistribution\Download folder will usually save over 1GB of space as it contains the installation sources for Windows Updates. Microsoft Update will re-download the files again if it needs them on the next update scan.
  3. C:\Users\<user>\AppData\Local\Temp

You can run defrag from within the VM, however if you are in a position where you can off-line compact the virtual disk, it is more time efficient to defrag the VHDX while offline.

Optimising Linux

Optimisation should also be performed on Linux systems. Unlike with Windows, Linux self-clears its own Temp space on restart. You can also free space from the updates process using your package manager. The below example can be used to free space using apt:

sudo apt-get update
sudo apt-get autoremove
sudo apt-get autoclean
sudo apt-get clean

Under native Linux file systems, there is no concept of running a defragmentation. ext4 performs this automatically on behalf of the system. This optimisation does not release free space in a “physical” fashion on the hard drive. Unless this “physical” space is released (zeroed out), Hyper-V will be unable to compact the disk.

Fortunately it is possible to force Linux to zero-out unused disk space in the VM. It can be performed using the following command

su
cd /
cat /dev/zero > zero.dat ; sync ; sleep 1 ; sync ; rm -f zero.dat

This command creates a file on the drive mounted in the “cd /” line. It then writes 0’s into this file until the system literally runs out of disk space. The new 0’s file is then deleted. If you are compacting a VHDX that is not the root partition, you must change the “cd /” line to represent the correct drive e.g. “cd /mnt/myDisk“.

Note: You will completely fill the volume for a few seconds. This will impact other write activities occurring on the disk and so can be considered to be a dangerous process.

 

Shrinking an Online VHDX

It is possible to perform an online compaction of a virtual disk. Hyper-V itself performs light-touch background optimisation automatically. If you cannot shutdown a VM and can only optimise an online VHDX then you must:

  1. Delete temp files
  2. Internally defragment the disk from within the VM itself
  3. Use Disk Management or diskpart to shrink the size of the mounted partition currently in use on the VHDX
diskpart
list vol
sel vol #
shrink
  1. Perform the compact using Hyper-V Manager or PowerShell
    Optimize-VHD <path to VHDX> -Mode Full
  2. Reverse the reduction in the size of the partition using Disk Management or diskpart
diskpart

list vol
sel vol #
extend

 

Shrinking an Offline VHDX

The most efficient method to free space from a VHDX file is to perform the compact wile it is offline. The disadvantage of an offline compaction is that the VM will need to be shutdown prior to the operation. The amount of time that the VM will be down for is directly proportional to the amount of work required to complete the optimisation process. You can improve this through online defragmentation prior to starting, however this takes significant additional administrative effort.

The following steps outline the process that I use to greatest effect. I use X:\ as the example drive letter in this scenario and the use of PowerShell is expected.

  1. Get the initial VHDX size
    $sizeBefore = (Get-Item <path to VHDX file>).length
  2. {optionally} Defrag the VM while online
  3. Shutdown the VM
  4. Mount the VHDX in read/write mode (not read only mode)
    Mount-VHD <path to VHDX file>
  5. Purge Temp files and the contents of X:\Windows\SoftwareDistribution\Download
  6. Defragment the VHDX while mounted to the management system
    1. If the VHDX is stored on SSD drives
      defrag x: /x
      defrag x: /k /l
      defrag x: /x
      defrag x: /k
    2. If the VHDX is stored on Hard Drives (/x /k /l are retained for Trim capable SANs)
      defrag x: /d
      defrag x: /x
      defrag x: /k /l
      defrag x: /x
      defrag x: /k /l
      Note: Defrag /d  can be particularly time consuming
  7. Dismount the VHDX
    Dismount-VHD <path to VHDX file>
  8. Perform a full optimisation of the VHD file
    Optimize-VHD <path to VHDX file> -Mode Full
  9. Get the new size of the VHDX
    $sizeAfter = (Get-Item <path to VHDX file>).length
  10. Start the VM
  11. Find out how much disk space you saved (if any)
    Write-Host "Total disk space Saved: $(($sizeBefore - $sizeAfter) /1Mb) MB" -Foreground Yellow

 

You will note that I repeat the steps of running defrag /x and defrag /k /l. In experimenting, this is because the repitition appears to allow a small amount of additiona space to be freed in some situations as show in the table below.

 

Results

Efficiency Purgable slabs
Size at start 73,991,716,864 100% 11
/k Slab consolidation 69,965,185,024 100% 11
/l Retrim 69,965,185,024 100% 11
/x Free space consolidation 69,965,185,024 100% 9
/x /l /k (repeat) 69,898,076,160 100% 9

The table shows the first /l retrim operation reducing the number of purgable slabs, after which a further 67,108,864 bytes (64MB) of space is freed – the two 32MB slabs.

 

Why not run Defrag /d on an SSD?

Defrag /d aka “traditional defrag” physically moves the file data to the end of its home partition, reconstructs the file in a contiguous series of blocks and moves the file back to the start of the disk. This process is unnecessary on an SSD. Here, there is virtually no likelihood that the data is stored in a contiguous fashion on the SSD NAND flash. There is also no performance benefit for the file being stored contiguously. While you can perform defrag /d on an SSD. In reality, you are needlessly shortening its cell-write life and the step should be skipped.

 

Conclusion

It is unfortunate that the process of compacting a VHDX file is not a seamless one. To realise the highest returns, it is necessary to shutdown the VM; which may not be practical in many scenarios. Equally, the amount of time required to perform the offline compact scales with the utilisation size of the VHDX, number of files and number of tasks performed as part of the maintenance.

Done right, and with the help of script automation, it can be a valuable task – especially before planned VM moves. I regularly save over 130GB in total when draining a hypervisor for maintenance in my home lab – around 25-30 minutes less file copy time over 1Gbps Ethernet. A worthwhile saving as it only takes 20 seconds to execute the automation script that does the work for me.

Sniffing the Parent Partitions Network Traffic in a Hyper-V Virtual Machine

C:Amie/ / Hyper-V, Microsoft, Networking, Windows Server

This article discusses a situation whereby you want to monitor/mirror/sniff network port traffic on a Hyper-V Parent Partition inside on of its own child VM’s.

Why would you need to do this?

Under a traditional architecture you have the flexibility to tell your switch to mirror all traffic into or out of Port 6 onto Port 21. You then connect a laptop to Port 21 and promiscuously monitor the traffic coming into that port. Under a modern Converged/Software Defined Network architecture, this will not work.

In a modern Converged Fabric design, physical NICs are teamed. The parent partition on the hypervisor no-longer uses the physical NICs, but logically uses its own synthetic NICs for data transfers.

  1. Link Aggregation/LCAP/EtherChannel will split the traffic at the switch
  2. Teaming/LBFO will split the traffic at the hypervisor
  3. Data security will fire a red flag as you will be monitoring too much unrelated traffic
  4. If you combine them, you will overload the monitoring Port with aggregated traffic, causing performance issues and packet loss
  5. You may impact the performance of tenant VM’s and mission critical services

Fortunately the Parent Partitions own Virtual NICs are identical to the vNICs in any Hyper-V virtual machine. Consequently, you can use the same Hyper-V functionality on the Parent Partition as you would any VM.

 

Requirements

In order to sniff traffic on the Parent Partition you must ensure the following:

  1. The Parent Partition and the VM must be connected to the same Virtual Switch
  2. The “Microsoft NDIS Capture” extension must be enabled on the Virtual Switch (this is enabled by default)
    Enable the Microsoft NDIS Capture Extensions
  3. The monitoring VM should have 2 vNICs. The vNIC used to monitor traffic should be configured onto the same VLAN as the vNIC on the Parent Partition. The monitoring NIC should have all of its service and protocol bindings disabled to ensure that only port mirrored traffic is appearing in the WireShark logs
    Disabling service and protocol bindings on the vNIC
  4. Wireshark, Microsoft NetMonitor or another promiscuous network traffic monitor
  5. If you are in a corporate environment, ensure that you have approvals from your Information Security team. In some jurisdictions port sniffing can be considered an offence

 

Enabling Port Sniffing

You cannot enable Port Sniffing on the Parent Partition using the Hyper-V Manager GUI. Open PowerShell on/to the Parent Partition

Execute Get-NetAdapter

Identify the name of vNIC that you will sniff traffic to/from e.g. vEthernet (Management)

Taking only the value inside the parenthesis "Management" enter the following command

Get-VMNetworkAdapter -ManagementOS 'Management' | Set-VMNetworkAdapter -PortMirroring Source

Substituting WireSharkVm for the name of your monitoring VM. Execute Get-VMNetworkAdapter 'WireSharkVm'

Identify the MAC Address of the vNIC’s that you will use to receive the Port Mirror from the Hyper-V host and enable it as the recipient for the mirror

Get-VMNetworkAdapter 'WireSharkVm' | ?{$_.MacAddress -eq '001512AB34CD'} | Set-VMNetworkAdapter -PortMirroring Destination

If the Parent Partition and VM vNICs are in the same VLAN. You should now be able to sniff traffic inbound to / outbound from the Parent Partition.

 

Disabling Port Sniffing

When using Port Mirroring, remember that it consumes CPU time and network resources on the hypervisor. To disable the port mirror, repeat the above commands substituting ‘None’ as the key-word for the PortMirroring parameter e.g.

Get-VMNetworkAdapter -ManagementOS 'Management' | Set-VMNetworkAdapter -PortMirroring None
Get-VMNetworkAdapter 'WireSharkVm' | ?{$_.MacAddress -eq '001512AB34CD'} | Set-VMNetworkAdapter -PortMirroring None

Removing phantom “ms-resource:AppName/Text” apps from the Start Menu

C:Amie/ / Microsoft, Windows Deployment

This article discusses a method of eliminating phantom “ms-resource:AppName/Text” entries on the Windows 10 Start Menu. You may see these after upgrading Windows 10 to version 1903 in an “other” group at the bottom of the Start Menu.

 

What are “ms-resource:AppName/Text” entries?

A database is used to store information on user-available ModernApps and its contents merged with traditional apps (.lnk files) when the start menu is opened by a user.

The “ms-resource:AppName/Text” reveals a corrupt/orphaned entry in the database. As part of this, lookups are performed to C:\Users\<username>\AppData\Local\Packages and/or C:\Windows\SystemApps to load the app’s manifest.xml file. The manifest file is used to query for the Icon, life tile instructions and the multilingual label used on the start menu.

If the database record exists, but the application itself no longer does – due to a crash during uninstall or the user being offline when an administrator removed the app. “ms-resource:AppName/Text” will appear until such time that Windows validates the contents of the database. This usually during the next update to the “Start Menu” app itself, or an OS upgrade.

 

Ensure App Uninstallation

A common reason for this occurring is:

  1. The user has never run the app to install it into their user profile
  2. The app is removed from AppxProvisionedPackages in C:\Windows\SystemApps by an administrator. This prevents self-repair
  3. The app is removed from ‘All Users’ on the system, however the database entry remains in one or more local user profiles

If there are remnants of the app in Get-AppxPackage or Get-AppxPackage -AllUsers, you must remove the entries first. This is because the entry will be re-written to the Start Menu database after it is reset.

Once the app has been removed from the local user account, ‘all users’ and the provisioned apps repository. You can reset the database.

 

Reset the Start Menu database

There are several ways to do this. This fix runs in the local user context and uses a “bludgeoning” approach to solving the problem.

Paste the following code into a PowerShell window. It will error, it will not be pretty but it will remove the phantom entry – provided that you have genuinely uninstalled the app.

Stop-process -Name 'explorer'; Remove-Item "$env:LocalAppData\Packages\$($(Get-AppxPackage | ?{$_.name -like '*startmenue*'}).PackageFamilyName)\TempState\" -Recurse -Force -Confirm:$false; Stop-process -Name 'explorer'; Remove-Item "$env:LocalAppData\Packages\$($(Get-AppxPackage | ?{$_.name -like '*startmenue*'}).PackageFamilyName)\TempState\" -Recurse -Force -Confirm:$false; Stop-process -Name 'explorer'; Remove-Item "$env:LocalAppData\Packages\$($(Get-AppxPackage | ?{$_.name -like '*startmenue*'}).PackageFamilyName)\TempState\" -Recurse -Force -Confirm:$false; Stop-process -Name 'explorer'; Remove-Item "$env:LocalAppData\Packages\$($(Get-AppxPackage | ?{$_.name -like '*startmenue*'}).PackageFamilyName)\TempState\" -Recurse -Force -Confirm:$false; Start-Process 'c:\windows\explorer.exe';

If you are paying attention, yes, the above is repeating itself several times. This is intentional.

 

What does it do?

Very simply the above PowerShell sample:

  1. Crashes the Windows Shell (Windows Explorer)
  2. Looks up the version number of the Windows 10 Start Menu app (“Microsoft.Windows.StartMenuExperienceHost”)
  3. Uses the version number to construct the path to the location of the Start Menu database
  4. Deletes the database
  5. Return to 1
  6. Repeat…
  7. Start Windows Explorer

The code repetition prevents explorer.exe from being auto-recovered by the WinLogon watchdog. If explorer.exe is running, it will fail to delete the database. By repeatedly running, it will eventually brute-force explorer.exe closed, perform the deletion and restart explorer.exe on its own.

Explorer.exe re-scans the local system/user to inventory apps when it starts and a new database created without the phantom app.

Redesigning the Hardware for the Virtual TV Streaming Server

C:Amie/ / Hardware, Hyper-V, Microsoft, Multimedia, Software

This article discusses a hardware design change to the Virtual TV Streaming Server discussed in Creating a Virtual TV Streaming Server.

If you are not familiar with the previous setup. The design revolved around an array of TV tuners connected to a 7-port USB 3.0 hub. In turn, this connected to a USB 3.0 controller which was passed through Discrete Device Assignment (DDA) through to a Windows 10 Virtual Machine. This run DVBLogic TV Mosaic, the IP TV streaming software.

 

Virtual TV Streaming Server Meltdown

The solution has run extremely well. There have been no crashes from TV Mosaic, the VM or the Hypervisor. Until last week.

The system missed last Saturdays recording schedules and on Sunday afternoon, wouldn’t initiate playback. On inspection of the VM, one of the Tuners was showing as “unknown” on the TV Mosaic console. The others were all fine. Once this phantom tuner was removed from the console, everything started working again.

Initially thinking that it was related to a coincidental BIOS update on the server, it turned out that the tuner was simply dead. I RMA’d it with DVBLogic – who didn’t challenge my diagnostic or offer any resistance – but I did have to ship it Internationally at my own expense.

A week later, I came to use the system again and, once more, it was dead. A trip to the attic later and the was dead. A multimeter confirmed that the power supply had died, and I begun an RMA process with StarTech this morning.

 

Analysis

If the power supply on the StarTech was defective, it could potentially have caused the fault with the TV Butler tuner. Although this is speculative and unprovable. My main suspicion is that the problems were caused by heat. The attic roof space is uninsulated, and the UK is in the summer period. With temperature in the attic space certainly to have ranged into the 40c’s.

Unlike with the physical TV server that this setup replaced – which had fans. This setup doesn’t. PCIe TV Tuners are intrinsically designed to withstand higher thermal variances than USB ones. The StarTech and TV Butler products are quite simply basic consumer devices. It is possible that this factor led to both of their demises.

There was a power outage mid-week last week, and the StarTech itself was not sitting on the server UPS – but it was on a surge protector. It is my belief that this did not contribute to the issue.

 

Hardware Redesign

The brief for the redesign is simple

  1. Remove essential electrical components from the attic
  2. Minimise space use
  3. Minimise electrical consumption (as everything will now be powered through the UPS)
  4. Do not clutter up the backplane of the server with dongles

 

Power

To accommodate #1, #2 and #3 the USB Hub is going to be eliminated from the design. The TV Tuners will now connect directly to the DDA USB controller. In order to do this, the dual port controller will need to be replaced.

After deliberating on whether to get an externally powered or bus powered 4-port controller, I chose a , bus powered card. A risk, given my previous experience here. The DG-PCIE-04B reviewed better than a similarly priced externally powered one. The decider was that it uses a NEC chipset and not a RealTek/SiS (i.e. cheap) chip. Finally, the fact that each of the ports had its own voltage management and fuse circuit is a valuable quality safeguard.

 

Patch Panel TV

To satisfy design brief #4, the USB TV Tuners will need to be mounted away from the server. To achieve this, I am going to mount the Tuners in the patch panel.

Using a set of keystone jacks. A USB lead will run between the USB controller and the Patch panel; simply mounting to the TV Tuners held in the patch panel.
TNP USB 3.0 Keystone Jack Image

The patch panel happens to be near the ceiling, directly above the TV aerial distributor for the house. Using 4m coaxial cable, the aerial feed can route through the existing ceiling cable run and clip neatly into the TV Tuners.

The Amazon order consisted of

  • 1x
  • 1x Pack of 5
  • 4x Rankie USB 3.0 Type A Male to Male Data Cable, 3m (Server – Patch Panel)
  • 3x Ex-Pro White Coax F Plug Type – to – Male M Coax plug Connection Cable Lead – 4m (Aerial distributor – TV Tuners)

 

Installation

The installation was extremely simple.

  1. Replace the existing 2 port USB controller with the 4 port one
  2. Clip the USB 3.0 keystones into the patch panel
  3. Run cables between the USB controller and the front profile (base) of the USB keystones
  4. Passing the USB controller through to Hyper-V
    1. Shutdown the Virtual Streaming TV Server VM
    2. Get the Device Instance Path from the Details tab > Device instance path section in Device Manager e.g.
      PCI\VEN_1912&DEV_0014&SUBSYS_00000000&REV_03\4&1B96500D&0&0010
    3. Use PowerShell to dismount the USB Controller from the Hypervisor and attach it to the VM
$vmName = 'TvServer'
$pnpdevs = Get-PnpDevice -PresentOnly | Where-Object {$_.InstanceId -eq 'PCI\VEN_1912&DEV_0014&SUBSYS_00000000&REV_03\4&1B96500D&0&0010'}
$instanceId = $pnpdev.InstanceId
$locationPath = ($pnpdevs[0] | get-pnpdeviceproperty DEVPKEY_Device_LocationPaths).data[0]
Write-Host "    Instance ID: $instanceId"
Write-Host "    Location Path: $locationpath"

# Disable the Device on the Host Hypervisor
Disable-PnpDevice -InstanceId $instanceId -Confirm:$false

# Wait for the dismount to complete
Start-Sleep -s 15

# Dismount the Device from the Host Hypervisor
Dismount-VmHostAssignableDevice -locationpath $locationPath -Force

# Attach the PCIe Device to the Virtual Machine
Add-VMAssignableDevice -LocationPath $locationpath -VMName $vmName

# Note: You may need to reboot the Hypervisor hosts at this point.
# If the VM's device manager informs you that it can see the controller, but is  unable to initialise
# the controllers USB Root Hub. A reboot should fix it.
  1. Clip the DVBLogic TV Butler TV Tuners into the patch panel USB keystone jacks using the inside (top) port on the keystones
  2. Start the TV Server VM
Photograph of USB Tuners mounted in patch panel
The patch panel now has three USB ports – the left-most TV Butler is missing as the RMA replacement has not yet arrived.

Photograph of USB Tuners mounted in patch panel Photograph of USB Tuners mounted in patch panel

The Virtualised Windows 10 Streaming TV Server came back online and there hasn’t been any instability caused by the bus-powered USB controller. The TV Butler’s are warm to the touch, have plenty of air-flow and the ambient temperature can be monitored via existing sensors in the room.

The completed assembly in the Patch Panel

With any luck, I will not need to revisit this project for quite some time!