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XenClient Enterprise 4.5. Engine Disks and Encryption. Table of Contents. Disk Encryption Overview. Disk Encryption Features Resources are protected at the logical volume layer. All Virtual Machine (VM) disks, engine configuration data, and log files.

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Engine disks and encryption

XenClient Enterprise 4.5

Engine Disks and Encryption

Disk encryption overview
Disk Encryption Overview

  • Disk Encryption Features

  • Resources are protected at the logical volume layer.

    • All Virtual Machine (VM) disks, engine configuration data, and log files.

    • Encryption remains intact if the disk is removed from the computer.

  • Easy to configure and manage Encrypted computers.

    • Encryption is an install-time option, no further configuration required.

    • Encryption does not impact management operations in Synchronizer.

  • Minimal impact to end-users.

    • No understanding or awareness of encryption is required.

    • Minimal impact on overall VM performance for most typical use cases.

  • Encryption Standards and Technologies

  • AES 256-bit encryption (specifically, AES-CBC-ESSIV with SHA256 hash).

  • Uses standard Linux modules (dm-crypt, lvm2, LUKS, etc).

  • What is not Supported Yet

  • Integration with Intel vPro trusted boot features (TXT/TPM).

  • Smart cards or two-factor authentication to unlock encryption.

  • These are features under consideration for a future release.

Disks partitions volume groups and volumes
Disks, Partitions, Volume Groups, and Volumes

Boot Volume (primary)

Boot Volume (secondary)

Root Volume (primary)

Root Volume (secondary)

Swap Space Volume

Log Volume

Engine Repository Volume

Hard Disk


Volume Group

Logical Volumes

XCE Engine only supports a single hard drive per computer.

Up to 4 primary partitions. XCE Engine only uses one partition. Others might be used to dual-boot another operating system.

The partition containing the Engine installation is configured into a LVM Logical Volume Group.

Several logical volumes are created within the group containing different parts of the XCE Engine installation.

Logical volume summary
Logical Volume Summary

*If the disk encryption option is chosen during Engine installation.

Why is not the boot volume encrypted
Why is not the Boot Volume Encrypted?

  • Boot Volume Does Not Require Encryption

  • Boot volume does not contain any data that requires encryption.

  • All sensitive data is stored in encrypted volumes.

  • Contents of boot volume cannot be used to unlock encrypted volumes.

  • Engine Cannot Boot Encrypted Partitions

  • Booting from encrypted volumes is not currently supported.

  • This is an area of investigation for a future release.

Encrypted vs unencrypted installation
Encrypted vs. Unencrypted Installation

  • Encryption status is set when Engine is installed.

  • Cannot change encryption status after installation.

  • Enabling or disabling encryption requires a full Engine reinstall.

Checking computer encryption status
Checking Computer Encryption Status

  • In the Engine Control Panel

  • Start the Engine control panel.

  • Select the “Tools by Category” view.

  • Start the “System Summary” applet.

  • The encryption status appears in the Hardware section.

  • In the Synchronizer Console

  • Locate the computer in the navigation panel.

  • Select the “Summary” tab.

  • The encryption status appears in the General section.

  • After Rebooting a Computer

  • If the Engine asks for a username and password, then encryption is not enabled.

  • If the Engine only asks for a password, then encryption is enabled.

How many bytes in a gigabyte
How Many Bytes In a Gigabyte?

Disk Manufacturers

1 GB = 1,000,000,000 (109) bytes


1 GB = 1,073,741,824 (230) bytes

  • XenClient Enterprise uses the Windows standard.

  • The difference is about 7%.

  • Must account for this difference when sizing hard drives.

  • Might be significant for smaller drives (especially SSDs).

Engine disk sizing calculations
Engine Disk Sizing Calculations

  • This is a rough calculation designed to give a conservative estimate of the required computer disk space, based on the VMs that will be installed.

  • Start with 10 GB to account for disk space used by the Engine.

  • For each VM deployed from Synchronizer:

    • Add the size of the system disk multiplied by 2.0.

    • Add the size of the user disk multiplied by 1.5.

    • Add the size of the local disk.

  • For each VM installed locally on Engine:

    • Add the size of the system disk.

  • Add 10 GB if the Dock is enabled in the Engine policy.

  • Multiply the result by 1.07.

  • This calculation is designed to give a conservative answer that should minimize the risk of disk over-subscription under most circumstances. Actual disk space requirements might be significantly less, but can be difficult to predict.

Disk sizing example
Disk Sizing Example

For this configuration, a 250 GB disk (or larger) is recommended. This is a conservative figure designed to minimize the risk of disk over-subscription.

Before computer startup
Before Computer Startup

Computer Status

Engine installed, encryption configured, but computer powered off. Encrypted volumes remain locked when the computer is powered off, or if the disk is removed from the computer.

Networking Status

No networking (computer is powered off).

Boot Volume Status

Unlocked. The boot volume is always unlocked. There is no requirement to lock this volume.

Root Volume Status

Locked. The root volume is locked with the user password.

Repository Volume Status

Locked. The repository volume is locked with a key stored in the root volume, which is locked with the user password.

Boot Volume

Root Volume


Encryption unlock screen
Encryption Unlock Screen

Computer Status

After power-on, computer boots up just enough so the Engine can accept a password from the user.

Networking Status

Disabled. Engine does not start networking until the computer is fully booted.


Boot Volume Status


Root Volume Status

Locked. The root volume cannot be unlocked until the user provides the password.

Repository Volume Status


Boot Volume

Root Volume


User enters unlock password
User Enters Unlock Password

Computer Status

User enters the password. Engine uses the password to unlock the root volume.

Networking Status

Still disabled. Checking the password with Synchronizer or Active Directory is not necessary or possible. If the password can be used to unlock the root volume then it must be correct.



Boot Volume Status


Root Volume Status

Unlocked. Encryption is unlocked with the password provided by the user.

Repository Volume Status

Locked. This volume is not locked with the user’s password. It gets unlocked in the next boot phase.

Boot Volume

Root Volume


Repository volume unlock
Repository Volume Unlock

Computer Status

After unlocking the root volume, Engine reads a key from the root partition and uses the key to unlock the repository volume. The repository volume is not encrypted with the user password.

Networking Status

Still disabled. Networking is not enabled until Engine is fully booted.

Boot Volume Status


Root Volume Status

Unlocked. Engine reads the repository key from the unlocked volume.

Repository Volume Status

Unlocked. Engine uses the repository key to unlock the repository volume.

Boot Volume

Root Volume


Boot process complete
Boot Process Complete

Computer Status

Fully booted. User might start VMs or access the Engine control panel. Engine can communicate with and be managed by the Synchronizer.

Networking Status

Enabled. Networking becomes available when the Engine boot process is complete.

Boot Volume Status


Root Volume Status


Repository Volume Status

Unlocked. This volume contains VHD files for VMs which can now be started.

Boot Volume

Root Volume


Encryption setup
Encryption Setup

The following message is displayed when Engine sets up disk encryption. The encryption setup process should not be interrupted!

  • Initial Encryption Setup

  • Encryption is not initially setup when the Engine is installed.

  • A password is required to setup encryption.

  • Encryption setup is delayed:

    • Until the computer is registered to Synchronizer.

    • Or when a local password is set for unregistered computers.

  • Subsequent Encryption Setup

  • Encryption setup also happens when the user’s Active Directory password changes.

  • This is to keep disk encryption in sync with Active Directory passwords.

Password validation after encryption unlock
Password Validation After Encryption Unlock

Engine sends the encrypted password to Synchronizer for validation. For local users, Synchronizer can validate the password directly.

For domain users, Synchronizer validates the password with Active Directory.

Engine unlocks encryption and completes the boot process. Password is encrypted and cached in memory.

User provides password to Engine.







The Engine never communicates directly with Active Directory. Any operations that require Active Directory go through the Synchronizer.

Resetting encryption passwords
Resetting Encryption Passwords

If the encryption unlock password validation fails, the following process is used to synchronize the password between Engine and Synchronizer or Active Directory.

Active Directory password validation fails.

Or validation of a local password fails at the Synchronizer.

Engine clears the password cache.

The user is prompted to enter a new password.

New password is validated, password cache is updated, and encryption is setup with the new password.











At the end of this process, the AD password, the Engine password cache, and the encryption unlock password are all synchronized.

User prompt to change encryption password
User Prompt To Change Encryption Password

  • If the password validation process fails because of an invalid password:

  • Engine will lock the computer screen.

  • A message is displayed indicating the password has changed.

  • User must enter credentials which are validated with Synchronizer.

  • After validation, the new password is used to setup encryption.

  • When the computer reboots, use the new password to unlock encryption.

Unlock password vs active directory password
Unlock Password vs. Active Directory Password

Password for Encryption Unlock

The password used to unlock encryption must be the same password that was last used to setup encryption. No other password will work. But an unlock code is available at the Synchronizer if the password is lost or forgotten.

Encryption Password vs. Active Directory Password

Usually the encryption unlock password will be the same as the Active Directory password for the registered user. But they can get out of sync. This usually happens when the Active Directory password changes while the Engine is offline.

Current Password vs. Previous Password

If the encryption unlock password gets out of sync with the Active Directory password, it might be necessary to provide the previous password to unlock encryption. If the previous password is lost or forgotten, use the unlock code from the Synchronizer.

Encryption and networking
Encryption and Networking

Networking Status During Encrypted Boot

During encrypted boot, networking is not available until after encryption is unlocked. Engine network configuration data is stored in the encrypted volumes, so it cannot be accessed until after the volumes are unlocked.

Networking Status at Encryption Unlock Screen

When the computer has booted to the encryption unlock screen, there is no networking available. The password provided by the user cannot be validated with Synchronizer or Active Directory until later in the boot process, after the encrypted volumes are unlocked.

Password Validation for Encryption Unlock

It is not necessary for the Engine to validate the unlock password with Synchronizer or Active Directory. If the password can be used to unlock the encrypted volumes, then it must be correct.

Remote Access to Encrypted Computers

If you are managing an encrypted computer with the VNC remote helpdesk feature, be careful about rebooting the computer. When the computer reboots, it will pause at the encryption unlock screen until the password is entered. There is no networking available at this stage so the VNC remote helpdesk feature cannot be used to connect to the computer and unlock encryption.

Synchronizer unlock code
Synchronizer Unlock Code

The Synchronizer stores an alternate key for each encrypted computer that can be used to unlock encryption on the computer if the user forgets the password, or if an administrator is required to unlock a computer and the user is not available.

To request the unlock code from Synchronizer, select the computer in the navigation panel then click the “Unlock Code” action button. Only administrators with the “Super User” role should have access to this feature.

Encryption lockout
Encryption Lockout

  • User has 4 attempts to unlock encryption.

  • After the 4th unsuccessful unlock attempt:

    • The computer will pause for 30 seconds.

    • Then the computer will reboot.

  • The unlock count is reset after reboot.

    • The user is never permanently locked out.

Computer storage report
Computer Storage Report

A summary of disk space and disk usage for a computer is available in the Synchronizer console. Select the computer in the navigation panel then click the “Storage” tab.

Computer storage report results
Computer Storage Report Results

A sample computer storage report is shown below. This report only reflects VMs deployed from Synchronizer. Local VMs are not included in the report.

Total space
Total Space

  • Equal to the size of the volume group containing the Engine logical volumes.

  • Nearly equal to the size of the disk partition containing the Engine installation.

  • Nearly equal to the entire disk size for installations using the entire disk.

Engine space
Engine Space

  • Amount of disk space currently being used (or reserved for future use) by the Engine.

    • Including the Dock, but not including any other VMs.

  • Usually around 10 GB.

    • Could be larger if the Dock is used in a way that causes its VHD files to grow.

    • For example, downloading files in the Chrome browser, or writing data to the Dock file share.

Virtual machines space
Virtual Machines Space

  • About equal to “Total Space” minus “Engine Space”.

  • Represents the total space available within the repository volume for VMs.

    • Not including the Dock VHD files (they are part of Engine Space).

  • Calculated as follows:

    • Start with the total capacity of the repository volume,

    • Then subtract about 1.5 GB reserved for use by the Engine,

    • Then subtract the size of the Dock VHD files.

Vm space used
VM Space Used

  • VM Space Used

  • Actual amount of disk space currently being used by the disk within the repository volume.

  • For disks with multiple VHD files, this is the total size of all VHD files for the disk.

  • Percent of VM Space Used

  • This is “VM Space Used” expressed as a percentage of “Virtual Machine Space”.

  • These Numbers Might Be Larger Than Expected!

  • Might be much larger than what the VM reports as space used within the virtual disk.

  • Could even be larger than the logical size of the virtual disk.

    • If this happens to a system disk:

      • Synchronizer might have many versions of a VM image outstanding.

      • Check to see if VM image versions can be rolled up.

    • If this happens to a user disk:

      • Engine might have pending backups that cannot be uploaded.

      • Check for a network or storage issue that might be preventing backups.

Additional vm space required for growth
Additional VM Space Required for Growth

  • Additional VM Space Required for Growth

  • VHD files start out very small and grow as data is written into them.

  • This column reflects the additional space that would be used if the VHD files were to grow to maximum size.

  • These numbers are used to determine if the hard disk is over-subscribed or under-subscribed.

Summary results
Summary Results

Total extra space that would be used if all VHD files grew to maximum size.

Total current size of all VHD files for all VMs.

Current amount of free disk space available for new VMs or VM growth.

Indication of whether the disk is over-subscribed or under-subscribed. Keep the disk under-subscribed to avoid running out of disk space because of VHD growth.

Example of vhd growth with 30 gb local disk
Example of VHD Growth With 30 GB Local Disk

Initial VM Installation

Local Disk Fills Up

After Local Disk Cleanup

The local disk in the Windows VM is almost completely empty.

The user has written data to the local disk, causing it to fill up.

After disk cleanup, Windows reports significant free space available.

The VHD file for the local disk begins much smaller than the 30 GB logical size. VHD files start small and grow as required.

The VHD file has expanded to contain the data written to the local disk by the Windows VM.

The VHD file is still large. VHD files start small, and grow as required to a maximum size, but never get smaller.

Disk space reporting in the VM is not a reliable indicator of how much disk space is actually being used for the VM within the Engine.