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Disk Image

Using this Protected Item type may incur a Booster charge.

This feature requires Comet Backup 20.8.0 or later.

Comet supports taking disk image backups.

This backup type is only applicable when running on Windows. Disk Image backup on other operating systems is not currently supported by this Protected Item type.

When using the "Disk Image" Protected Item type, on the Items tab, you can select any currently-attached drives for backup, or individual partitions from any drive. It is possible to select "all drives" and exclude individual disks or partitions.

Any change to the partition structure of a drive will cause that drive to be recognized differently in Comet. If you had selected such a drive, Comet will warn you that the drive can no longer be found. You would need to reselect the drive and/or partitions in the Comet Backup app interface.

Comet feeds raw data from each disk partition directly into its chunking deduplication engine. The disk image is deduplicated, compressed, and encrypted as it is being saved to the Storage Vault. No extra temporary spool data is generated and no additional disk space is required.

The backed-up disk image data will deduplicate with other data inside the Storage Vault. A 'Files and Folders' type backup of the same data volumes should achieve a high degree of space savings. The effectiveness of any such deduplication may be negatively affected by: (A) filesystem fragmentation on the physical volume; and/or (B) small file sizes.

Comet does not allow additional file exclusions within a partition.

Operating system compatibiltiy

The "Disk Image" Protected Item type in Comet is only available with full functionality on Windows 7, or Windows Server 2008 R2, or later (including Windows 10 and Windows Server 2019). Older versions of Windows such as Windows Vista or Windows Server 2008 RTM may operate with limited functionality, including- but not limited to- the inability to skip over free space on some filesystem partition types.

Unused disk sectors

On supported filesystems, Comet will exclude unused space from the disk in the backup image. Unused space is represented as zero ranges, that are compressed during the backup phase. When restoring the disk image, the file will include uncompressed zero ranges. Please see the "Supported volume types" section for more information about what filesystems are compatible with this feature. You may disable skipping free space by enabling the "Include unused disk sectors for forensic data recovery" option.

The disk must be set as Online in Windows for Comet to exclude unused space. If the disk is set as Offline in Windows, Comet is unable to exclude free space, even from a supported filesystem. You can change a disk's Online/Offline state from Disk Management (diskmgmt.msc) or from diskpart.

If a disk extent does not contain a filesystem (e.g. if it is a raw byte range), then Comet is unable to determine which disk sectors are needed. If you select a "Raw byte range" extent, it is backed up in its entirety, even if the "Include unused disk sectors for forensic data recovery" option is selected. If the raw data contains mostly zero bytes, it will be highly compressed during the backup phase and when stored as chunks in the Storage Vault; however, if the raw data contains mostly random data, it will not compress well.

Comet always skips backing up the pagefile of the booted Windows installation (pagefile.sys / swapfile.sys), even if the "Include unused disk sectors for forensic data recovery" option is enabled.

Drive letter support

From version 24.3.7 you can now select disks/partitions by drive letter. Please note we recommend using the Live Picker over this method, however, this is useful for policies or for when you don't have a live connection to the device.

Selecting a drive letter that has only one mount point on the drive will include every partition on the drive for the backup. Meanwhile, if there are multiple mount points on the drive, only the partition of the selected drive letter will be backed up.

To access this option via the Comet Server web interface, when adding a Disk Image you must change the Type value to Include drive letter.

To access this option from the Comet Backup desktop app, on the Items tab you must first enable the option Select by Drive Letter (advanced), then swap to the Drive Letters tab.

Supported volume types

Please refer to the following table of filesystem support notes:

FilesystemSkip unused spaceConsistency
NTFS (Microsoft)YesSnapshot
ReFS (Microsoft)YesSnapshot
FAT32 (Microsoft)YesIf volume is not in use
exFat (Microsoft)YesIf volume is not in use
UDF (Microsoft)NoIf volume is not in use

Third-party filesystem drivers (e.g. WinBtrfs, Ext2Ifs, Paragon Linuxfs, ZFSin) have not been officially tested against Comet.

Please refer to the following table of special volume type notes:

Volume typeSupportedNotes
Basic disksYesFully supported
Dynamic disksYesThe underlying volume will appear as "Raw byte range". For a span or striped volume, you should make sure to only select the dynamic volume for backup, not the underlying raw disk. Please also note that Dynamic disks are deprecated in Windows 8 and above.
Storage SpacesYesThe underlying volume will appear as "Orphaned volume". You should make sure to select only the Storage Space for backup.
BitlockerYes, while unlockedThe backup can succeed if the Bitlocker volume is unlocked. If the Bitlocker volume is locked, it should be unlocked before running the backup job, otherwise you may experience an error This drive is locked by BitLocker Drive Encryption. You must unlock this drive from Control Panel.. The resulting partition backup is not protected by Bitlocker and you may extract single files from it without the Bitlocker encryption key, as described below. If you restore to a physical partition, you may wish to re-enable Bitlocker after restoring, via the Windows Control Panel.
Cluster Shared Volumenot testednot tested
Truecrypt / Veracryptnot testednot tested

Please refer to the following table of physical media notes:

Physical mediaSupportedNotes
Hard drive (512n)YesFully supported
Hard drive (AF)Yes512e and 4Kn (Advanced Format) harddrives are supported.
Mounted VHD / VHDXYesFully supported
Removable USB driveYesSome removable drives cannot be completely offlined by the operating system; a restore operation back to the physical removable USB drive may be interrupted by other programs on the PC.
Remote iSCSI LUNYesTested successfully against the Windows Server File and Storage Services iSCSI implementation
Mounted ISONoOnly harddrive (HDD / SSD) disks are supported.
Optical driveNoOnly harddrive (HDD / SSD) disks are supported.
Floppy driveNoOnly harddrive (HDD / SSD) disks are supported.

Please refer to the following table of partition table notes:

Partition tableSupportedNotes
MBRYesFully supported, including Extended partitions (EBR)
GPTYesFully supported

Consistency

Comet tries to take a VSS snapshot of the selected partition (without invoking any specific writers for quiesence). If this succeeds, the partition backup is crash-consistent.

Comet tries to lock the volume handle. If this succeeds, the partition backup is crash-consistent.

Otherwise, Comet will print a warning to the job log, and back up the partition in a rolling way. The backup may be inconsistent if other processes are writing to the partition at the same time.

Disk Image Backup Configuration Video Guide

Restoring

Comet stores the disk image files in VMDK format. You can restore these files normally using Comet.

There is one plain-text VMDK descriptor file representing metadata about the whole drive, plus separate raw image files for each partition's extent on the disk.

Partitions of the disk that were not selected for backup are represented as zero extents in the VMDK descriptor file. This means the restored disk image appears to have the full disk size, even if only a small amount of partitions inside it were selected. The zero extents will be compressed inside the Storage Vault.

On Windows, the Comet Backup desktop app offers the option to restore the disk images either back to physical partitions, or as files.

Recovery of single files, with spooling

You can restore the VMDK disk images and then extract single files from them.

At the time of writing, we recommend the following software:

  • 7-Zip
    • Free and Open Source, Windows (GUI) and macOS / Linux (command-line)
    • Can open VMDK disk descriptor and also the individual extent files
      • Supports many filesystems, including NTFS, FAT32, EXT 2/3/4, UDF, HFS, SquashFS
    • Known issues:
      • When loading the VMDK disk descriptor directly instead of the extent files, if no partition table is present (i.e. "Raw byte range" containing the MBR/GPT area at the start of the disk was not selected for backup) then the descriptor will only show an interior 'disk.img' file instead of partition contents
        • You can workaround this issue by opening the individual partition extent files
          • Early versions of 7-Zip had only limited support for disk image features. Please manually ensure your 7-Zip installation is up-to-date, as 7-Zip does not have a built-in software update feature.
  • DiskInternals Linux Reader
    • Freeware, Windows-only
    • Despite the product name, also supports Windows filesystems (NTFS, FAT)
    • Can mount VMDK files as a drive letter
      • from the menu > Drives > Mount Image > "VMware virtual disks (*.vmdk)"
    • Known issues:
      • Fails to open the VMDK disk descriptor if there is junk data in "Raw byte range" areas.
        • You can workaround this issue by editing the descriptor file to replace these with zero extents.
        • e.g. edit disk.vmdk change RW 16065 FLAT "disk-f0000.vmdk" 0 to RW 16065 ZERO
  • Passmark OSFMount
    • Freeware, Windows-only
    • Can mount VMDK extent files as a drive letter
    • Known issues:
      • When loading the VMDK disk descriptor directly instead of the extent files, the disk partitions can be discovered, but mounting fails - both of the individual partitions and also when attempting to mount the VMDK as a raw disk ("Physical Disk Emulation" mode)
        • You can workaround this issue by selecting the individual extent files to mount (works using "Logical Drive Emulation" mode)
  • ImDisk Virtual Disk Driver
    • Freeware, Windows-only
    • Can mount individual RAW extents
    • Can parse the VMDK disk descriptor, scanning for disk volumes, and allows mounting them individually
    • Not able to mount the VMDK as a whole physical disk, only able to mount its discovered volumes
  • VMware Workstation
    • Commercial software with free trial available (Windows / macOS / Linux)
    • Has a feature to mount VMDK files as a local drive letter. From the "File" menu, choose "Map Virtual Disks"
    • See more information in the VMware Documentation (docs.vmware.com).
  • Guestfs
    • Free and Open Source (Linux-only, command-line)
    • Install the guestfs-tools package (Debian/Ubuntu: libguestfs-tools, SuSE: guestfs-tools, RHEL/CentOS/Fedora: libguestfs-tools-c)
    • Supports mounting the VMDK disk descriptor file using an unprivileged FUSE backend
      • Usage: guestmount -a disk.vmdk
  • Loop device
    • Free and Open Source (part of the Linux kernel, command-line)
    • Use the losetup tool (from util-linux)
    • Supports mounting individual partition extents, but not the VMDK disk descriptor file

Recovery of single files, without spooling

Supported from 22.12.5. See the Disk Image guide for more details.

Booting into a recovered Windows OS installation

When migrating a Windows OS installation to different hardware, any products which use hardware identifiers as a software licensing component may lose their activation status. This includes, but is not limited to

The "C:" does not contain everything needed to boot an operating system. For best results when creating a bootable image, you may wish to ensure that your backup includes

  • the disk's non-partition space (that includes the GPT/MBR partition table)
  • the "System Reserved Partition", if present (that contains the volume boot record)
  • the EFI ESP partition, if present (on GPT disks and/or UEFI-booting machines)

Windows 8.1, Windows 10, and later

Current versions of Windows do generally handle being booted on dissimilar hardware without any issues.

Earlier versions of Windows

When you boot a Windows OS installation, it may automatically become specialized for the running hardware (physical or virtual). This improves performance, but can prevent the same OS installation from booting on different hardware if the hardware is sufficiently different. The tolerable differences depend on the hardware in question.

If you experience errors booting a backed-up Windows OS disk image on different hardware (physical or virtual), it may be necessary to prepare the Windows installation for hardware-independence. You can do this by running sysprep inside the installation before taking the disk image; or, you can do this by booting a Windows recovery environment, mounting the image, and running sysprep against the attached disk.

The sysprep tool is installed in the C:\Windows\system32\Sysprep\ directory and is available on all Windows SKUs. From Windows 8.1 onward, its GUI is deprecated in favor of command-line use.

Filesystem smaller than target volume

When restoring a smaller partition into a larger one, Comet will automatically extend the restored filesystem to the fill the target partition. This feature is available on Windows if the filesystem driver supports it (the NTFS and ReFS file systems).

In other cases, the result will be a large partition containing a small filesystem. It appears to have the large size in Disk Management (that looks at the partitions) but the small size in This PC (that looks at the filesystem). The extra space from the new larger partition cannot be practically used until the filesystem is extended, to fill the partition around it.

On Windows, you can independently repeat Comet's attempt at manually extending the filesystem to fill its containing partition by

  1. opening Command Prompt as administrator
  2. run diskpart.exe
  3. type list volume
  4. Identify the target volume from the list, and then type select volume TARGET_NUMBER
  5. type extend filesystem

On Linux, you can resolve this issue by using the ntfsresize command.

Filesystem larger than target volume

Comet does not support restoring a large backed-up partition into a smaller physical partition. If you are trying to do this, please shrink the partition using the OS's partition manager prior to performing the backup.

Recovery to physical hardware

In order to restore to physical hardware, the target disk or partition should be unmounted. Comet Backup may be able to do this automatically from your current booted OS, if no programs are using the target drive (e.g. for a non-boot drive); but in order to restore to your boot drive, you should first reboot the PC into a recovery environment.

The Comet Backup desktop app supports creating a USB Recovery Media or an ISO image file from the wizard on the Account screen.

The following options are available:

1. WinRE USB

WinRE USB is the default option for creating Recovery Media within the Comet Backup desktop app.

Selecting this option allows you to create a minimal USB Recovery Media based on the Windows Recovery Environment. It requires a removable USB drive of at least 2GB in size and up to 32GB. The size requirements may be larger if additional drivers get installed into the image.

This option requires that Windows Recovery Environment is installed and available on your PC. If it is not installed, you may be able to install it via the reagentc /info command.

If you choose to create a WinRE drive from inside the Comet Backup desktop app, the resulting USB drive is created as follows:

  • Choose an available removable USB drive
  • Select options
    • You can choose whether the current OS drivers are embedded into the image
      - This feature extracts in-use third-party drivers from the current OS using the `dism /export-driver` technology. The exact selected drivers may depend on your running OS. In our experience it mostly includes OEM drivers. The included drivers could be of any type (chipset/network/graphics/audio/usb/pcie/storage/...). There are no guarantees about what drivers will be added, but it should generally be helpful in making sure you can use the device.
      • You can choose to add (slipstream) additional drivers and programs into the image
        • You can add drivers in *.inf file format. This is the standard file format for driver installation packages on Windows. When choosing this option, the Comet Backup desktop app will open a file picker to the C:\Windows\System32\DriverStore\FileRepository\ directory that contains most currently-installed driver packages on the current PC.
        • You can add custom files and folders. These will be copied to the resulting media under the virtual X:\custom\ directory.
        • You can add a custom command to run during startup. For instance, this may be useful to run any driver installer that was only available as a custom installer exe file. Because custom files and folders are copied under the virtual X:\custom\ directory, your resulting custom command to run should take the form X:\custom\my-installer.exe.
        • The most recent successful settings are preserved in the Windows registry for the next use.
  • The drive is created
    • No additional download is required to create the drive
    • The drive uses a hybrid MBR/EFI boot and should boot correctly on both MBR and UEFI PCs
    • The drive uses the Microsoft ntldr bootloader and should boot correctly on UEFI PCs requiring Secure Boot. If you experience issues booting the USB Recovery Media drive, you could try to temporarily disable Secure Boot from your UEFI firmware menu
    • The drive preserves the custom branding of the installed Comet Backup application
    • The drive impersonates your own Device ID and will appear to Comet as the same device (when booted on the same physical hardware)
    • The drive will be either x86_32 only, or x86_64 only, depending on your installed Windows OS version
    • When booting the drive, the Comet desktop app will appear directly. You can use Comet to restore data. When exiting Comet, the Windows Recovery Environment will appear, allowing you to perform any other pre-boot tasks (e.g. boot repair or access Command Prompt) before rebooting the PC normally.
      • Note: Set the timezone to the appropriate one, using the tzutil command, then adjust the date and times with the date and time commands. A device which is out-of-sync with internet time may experience difficulties with backups to some cloud storage providers.

Limitations

When using a USB-boot environment, the available hard-drives are enumerated as-found. If a local-path Storage Vault has been used for backups, sometimes the listing of drives will correspond to drive-letter-mappings in the existing Windows system, but when it does not, the drive letters will need to be explicitly set.

Setting the newly-enumerated drive-letters:
  • Boot using the USB
  • Drop into the command-line via 'Tools' -> 'Command Prompt'
  • type DISKPART to start the program
  • type LIST VOLUME to show all available volumes and their current drive letters
  • identify which volume is the one which needs to be reassigned the label 'F' (e.g. volume 5)
  • type SELECT VOLUME 5
  • type ASSIGN LETTER=F
  • type LIST VOLUME to verify

Usage of UNC paths for Storage Vault locations, rather than drive-letters, normally avoids this issue

Some features are currently unavailable from inside the created WinRE USB drive:

  • Wifi support
    • Workaround: Connect to the network via wired Ethernet instead
    • Alternative workaround:
      1. Find the currently used driver for your hardware's Wifi adapter (device manager - network adapters - find wifi adapter - properties - driver tab - 'driver details' button - get file name as *.sys)
      2. In Comet's USB Recovery Media wizard, choose 'add custom driver', find the folder with the same name as the *.sys driver and choose its *.inf file
      3. Boot the Comet USB Recovery Media drive and open a Command Prompt
      4. Start the Wifi subsystem using net start wlansvc
      5. Ensure that the wifi network interface appears in netsh wlan show interfaces
      6. Browse wifi Access Points using netsh wlan show networks and connect to one
  • VSS for backup operations
    • Workaround: It should not be necessary to use VSS for backup operations from inside the WinRE boot environment
  • The Windows Disk Management GUI
    • Workaround: Use diskpart commands

The resulting WinRE USB drive is based on your PC's version of WinRE. WinRE is provided and updated by Microsoft and contains a version of the Windows kernel that is specific to the latest feature upgrade (e.g. 1903 / 1909 / 2004). For best results when using the "fix Windows boot problems" feature after a full disk restore, you should avoid using an old USB Recovery Media drive for a newer version of Windows (e.g. using a 2004-based WinRE should be able to boot-repair a 1903-based Windows installation, but perhaps not vice-versa).

2. WinRE ISO

WinRE ISO is the option for creating an ISO image file within the Comet Backup desktop app.

Selecting this option allows you to create a minimal ISO image file based on the Windows Recovery Environment.

This option requires that Windows Recovery Environment is installed and available on your PC. If it is not installed, you may be able to install it via the reagentc /info command.

If you choose to create an ISO image file from inside the Comet Backup desktop app, the resulting ISO image file is created as follows:

  • Choose a target ISO image file
  • Select options
    • You can choose whether the current OS drivers are embedded into the image
      - This feature extracts in-use third-party drivers from the current OS using the `dism /export-driver` technology. The exact selected drivers may depend on your running OS. In our experience it mostly includes OEM drivers. The included drivers could be of any type (chipset/network/graphics/audio/usb/pcie/storage/...). There are no guarantees about what drivers will be added, but it should generally be helpful in making sure you can use the device.
      • You can choose to add (slipstream) additional drivers and programs into the image
        • You can add drivers in *.inf file format. This is the standard file format for driver installation packages on Windows. When choosing this option, the Comet Backup desktop app will open a file picker to the C:\Windows\System32\DriverStore\FileRepository\ directory that contains most currently-installed driver packages on the current PC.
        • You can add custom files and folders. These will be copied to the resulting media under the virtual X:\custom\ directory.
        • You can add a custom command to run during startup. For instance, this may be useful to run any driver installer that was only available as a custom installer exe file. Because custom files and folders are copied under the virtual X:\custom\ directory, your resulting custom command to run should take the form X:\custom\my-installer.exe.
        • The most recent successful settings are preserved in the Windows registry for the next use.
  • The ISO image file is created
    • No additional download is required to create the ISO image file
    • The ISO image file should boot correctly on both MBR and UEFI mode
    • The ISO image file should boot correctly on UEFI mode setting with Secure Boot. If you experience issues booting the ISO image file, you could try to temporarily disable Secure Boot from your UEFI firmware menu
    • The ISO image file preserves the custom branding of the installed Comet Backup application
    • The ISO image file impersonates your own Device ID and will appear to Comet as the same device (when booted on the same physical hardware)
    • The ISO image file will be either x86_32 only, or x86_64 only, depending on your installed Windows OS version
    • When booting the ISO image file, the Comet Backup desktop app will appear directly. You can use Comet to restore data. When exiting Comet, the Windows Recovery Environment will appear, allowing you to perform any other pre-boot tasks (e.g. boot repair or access Command Prompt) before rebooting the PC normally.
      • Note: Set the timezone to the appropriate one, using the tzutil command, then adjust the date and times with the date and time commands. A device which is out-of-sync with internet time may experience difficulties with backups to some cloud storage providers.

Some features are currently unavailable from inside the created WinRE ISO image file:

  • Wifi support
    • Workaround: Connect to the network via wired Ethernet instead
    • Alternative workaround:
      1. Find the currently used driver for your hardware's Wifi adapter (device manager - network adapters - find wifi adapter - properties - driver tab - 'driver details' button - get file name as *.sys)
      2. In Comet's Recovery Media wizard, choose 'add custom driver', find the folder with the same name as the *.sys driver and choose its *.inf file
      3. Boot the Comet Recovery Media drive and open a Command Prompt
      4. Start the Wifi subsystem using net start wlansvc
      5. Ensure that the wifi network interface appears in netsh wlan show interfaces
      6. Browse wifi Access Points using netsh wlan show networks and connect to one
  • VSS for backup operations
    • Workaround: It should not be necessary to use VSS for backup operations from inside the WinRE boot environment
  • The Windows Disk Management GUI
    • Workaround: Use diskpart commands

The resulting WinRE ISO image file is based on your PC's version of WinRE. WinRE is provided and updated by Microsoft and contains a version of the Windows kernel that is specific to the latest feature upgrade (e.g. 1903 / 1909 / 2004). For best results when using the "fix Windows boot problems" feature after a full disk restore, you should avoid using an old ISO image file for a newer version of Windows (e.g. using a 2004-based WinRE should be able to boot-repair a 1903-based Windows installation, but perhaps not vice-versa).

3. Windows To Go

Windows To Go is an alternative option for creating USB Recovery Media within the Comet application.

Selecting this option allows you to create a full Windows boot environment. It requires an external harddrive of at least 32GB in size.

This option requires the Portable Workspace Creator (pwcreator.exe) to be installed and available on your PC. This tool is included in Windows Server 2012, Windows 8 Pro, Windows 8.1 Pro, Windows 10 Pro but was removed in Windows 10 update 2004 owing to the difficulty of deploying critical software updates to this platform.

No customisations are applied to the generated Windows To Go boot drive. You should boot into the drive, then install Comet normally and use it to perform recovery operations such as restoring data.

Other boot environment

You may also create a recovery environment in any other way. Either Windows or Linux can be used as a suitable recovery environment. Some possible methods include

  • creating a Linux bootable USB drive, or
  • using a third-party tool like Rufus to create a Windows To Go drive, or
  • using recovery media from your PC OEM vendor (e.g. Lenovo / Dell / HP)

In these cases you will need to manually launch the Comet Backup app once booted into the recovery environment.

Restore from Windows boot environment

From the Windows boot environment, run Comet Backup, and open the Restore wizard. The Restore wizard inside Comet Backup allows restoring the backed-up disks and partitions directly to your physical disks and partitions, without requiring any temporary spool space.

You can use the "edit" button to repartition the local drives using Windows Disk Management. After doing so, use the "refresh" button to refresh the local disks and partitions for restore.

To do so:

  1. Select a backed-up disk or partition to restore, from the left-hand pane
  2. Select a target disk or partition to write to, from the right-hand pane
  3. Click the "Add to restore queue" button
  4. Repeat steps 1-3 as necessary
  5. Click the "Restore" button to begin the restore job.

Restore from Linux boot environment

To restore an entire disk, with spooling:

Restore all the *.vmdk disk image files to a spool drive.

Convert the main vmdk descriptor file to a physical drive, using the following command: qemu-img convert disk.vmdk -O raw /dev/sdx

Alternatively, you can mount the main vmdk descriptor file as an NBD volume if your kernel has NBD support (you may need to modprobe nbd first):

qemu-nbd --connect /dev/nbd0 disk.vmdk
dd if=/dev/nbd0 of=/dev/sdx bs=8M status=progress

To restore an entire disk, without spooling:

  1. Restore just the disk.vmdk file (without the data extents), and open it in a text editor in order to read the partition sizes.
  2. Recreate partitions to the exact target size.
  3. Then you can restore single partitions without any local spool disk, using the "Program Output" restore option, and selecting only a single partition file for restore: dd of=/dev/sdx1 bs=8M

To restore a single partition, with spooling:

Recreate a partition to the exact target size.

Restore the target extent file (e.g. disk-f0000.vmdk)

Use dd to clone the selected extent file (e.g. disk-f0000.vmdk) to a physical partition (e.g. /dev/sdx1) as follows: dd if=disk-f0000.vmdk of=/dev/sdx1 bs=8M status=progress

To restore a single partition, without spooling:

Recreate a partition to the exact target size.

Select the file for backup, and use the "Program Output" restore option to stream the file into a command like dd of=/dev/sdx1 bs=8M, choosing a single partition only

Recovery to local VM

You can attach the *.vmdk disk image files to a new- or existing Virtual Machine. If the disk image contains a Windows OS installation, it may be bootable.

Virtualisation platformSupports Comet's *.vmdk file format
VMware Fusion / Player / WorkstationYes
VMware vSphereNo - Restore as VMware virtual disk to generate compatible disk images.
QEMUYes
VirtualboxYes
Hyper-VNo - must convert to VHD or VHDX format

If your PC boots using EFI - for instance, if the source disk contains an EFI System Partition (ESP) - then you should configure the VM to boot in EFI mode ("Generation 2" in Hyper-V). Otherwise, you should configure the VM to boot in "Legacy" / MBR mode ("Generation 1" in Hyper-V).

When planning to restore as a VMware vSphere virtual machine, backing up all disks and partition is recommended to ensure that the expected disk structure is intact.

Converting VMDK variant for VMware ESXi

VMware ESXi supports booting a restored Disk Image from a Comet backup job (Physical-to-virtual / P2V). However, the VMDK file format used by Comet uses multiple extents, which is not supported by ESXi until it is converted first.

You can boot your restored Comet disk image vmdk files in ESXi following these steps:

  1. Make Comet's restored vmdk files accessible to your VMware Datastore.
    • For instance on a single ESXi server, you can upload the files through the Datastore browser; or on a SAN environment, you can copy them out-of-band to the SAN storage.
  2. SSH into the ESXi server.
    • You can temporarily enable SSH from the ESXi web console.
  3. Enter the datastore directory containing the restored Comet vmdk files: cd /vmfs/volumes/my-datastore-name/path-to-comet-disk-images/
  4. Start to convert the disk. vmkfstools -i ./disk.vmdk converted.vmdk -d thin
    • This will require additional temporary disk space, up to the size of the disk image.
    • You can replace -d thin with -d zeroedthick to preallocate the full disk size. For more information on the available VMDK types, see VMware's documentation.
    • Once the conversion has completed, you should see a new converted.vmdk and converted-flat.vmdk files.
  5. Delete the original Comet vmdk files: rm ./disk*.vmdk
  6. Continue to configure the ESXi virtual machine
    • on the Virtual Hardware tab, ensure the converted disk is attached to the VM, not the original disk
    • on the Virtual Hardware tab, ensure it is connected to the SATA controller, not the SCSI controller
    • on the VM Options tab, ensure the VM is configured for either BIOS or EFI boot as appropriate

Converting VMDK to VHDX for Hyper-V

Hyper-V supports booting a restored Disk Image from a Comet backup job (Physical-to-virtual / P2V). However, Hyper-V does not support Comet's file format; it must be converted first.

You can convert Comet's vmdk files to Hyper-V-compatible vhdx files using qemu-img:

  1. Download qemu-img for Windows from qemu.org
  2. From a command prompt, run C:\path\to\qemu\qemu-img.exe convert -f vmdk -O vhdx C:\path\to\comet\disk.vmdk C:\path\to\output.vhdx -p
    • This will require additional temporary disk space, up to the size of the disk image.
  3. You may also need to run the command fsutil sparse setflag C:\path\to\output.vhdx 0 if you run into sparse file errors.
  4. Delete the original Comet vmdk files.

Recovery to cloud server

You can upload the *.vmdk disk image files to a cloud provider. Depending on the cloud provider's capabilities, it may be possible to boot a new VM from them, or to attach them as extra disks to an existing VM.

If the disk image contains a Windows OS installation, it may be bootable. Not all cloud providers support booting Windows OS installations.

ProviderSupports *.vmdk file formatInformation
Amazon EC2Yeshttps://aws.amazon.com/ec2/vm-import/
https://docs.aws.amazon.com/vm-import/latest/userguide/vmimport-image-import.html
AzureNo - must convert to VHD formathttps://docs.microsoft.com/en-us/azure/virtual-machines/windows/upload-generalized-managed
DigitalOceanYeshttps://blog.digitalocean.com/custom-images/
UpCloudYeshttps://upcloud.com/community/tutorials/import-vmware-images/

Converting Windows System to Disk Image

With the upcoming deprecation of our Windows System Protected Item type, we have implemented a way to automatically convert a Windows System Protected Item into a Disk Image Protected Item.

Please note that when the Windows System Protected Item type is deprecated this conversion will take place automatically as part of the Comet Server startup process.

The conversion is handled using our new user bulk action option on the Comet Server web interface. Simply navigate to the "Users" tab, select the users you would like to perform the conversion for, click the "Bulk Actions" dropdown button and select "Convert Window System Protected Items". A notification should display with the number of Protected Items that were converted.

For Windows System Protected Items that weren't backing up disks with only a single assigned drive letter, we recommend converting the Protected Item manually, as this conversion option only supports converting disks with a single drive letter.

Please note that the "All Critical Volumes" option is assumed as the C: drive.