1. Engine Disks and Encryption
XenClient Enterprise 4.5
Engine Disks and Encryption

2. Table of Contents Engine Disks and Encryption Engine Disk Sizing
Page 1
Table of Contents
Page 2
Disk Encryption Overview
Page 3
Disks, Partitions, Volume Groups, and Volumes
Page 4
Logical Volume Summary
Page 5
Why is not the Boot Volume Encrypted?
Page 6
Encrypted vs. Unencrypted Installation
Page 7
Checking Computer Encryption Status
Page 8
Engine Disk Sizing
Page 9
How Many Bytes In a Gigabyte?
Page 10
Engine Disk Sizing Calculations
Page 11
Disk Sizing Example
Page 12
Encrypted Boot Sequence
Page 13
Before Computer Startup
Page 14
Encryption Unlock Screen
Page 15
User Enters Unlock Password
Page 16
Repository Volume Unlock
Page 17
Boot Process Complete
Page 18
Encryption Setup and Passwords
Page 19
Encryption Setup
Page 20
Password Validation After Encryption Unlock
Page 21
Resetting Encryption Passwords
Page 22
User Prompt To Change Encryption Password
Page 23
Unlock Password vs. Active Directory Password
Page 24
Encryption and Networking
Page 25
Synchronizer Unlock Code
Page 26
Encryption Lockout
Page 27
Computer Storage Report
Page 28
Page 29
Computer Storage Report Results
Page 30
Total Space
Page 31
Engine Space
Page 32
Virtual Machines Space
Page 33
Virtual Machine Space Used
Page 34
Additional Virtual Machine Space Required for Growth
Page 35
Summary Results
Page 36
Example of VHD Growth With 30 GB Local Disk
Page 37

3. 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.

4. Disks, Partitions, Volume Groups, and Volumes
Hard Disk
Partitions
Volume Group
Logical Volumes
Boot Volume (primary)
Boot Volume (secondary)
Root Volume (primary)
Root Volume (secondary)
Swap Space Volume
Log Volume
Engine Repository Volume
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.

5. Logical Volume Summary
Encrypted*
Size
Description
Primary Boot No
128 MB
Boot volume for the current version of XCE Engine.
Secondary Boot
Boot volume for the previous version of XCE Engine.
Primary Root
Yes
2048 MB
Contains the dom0 root file system for the current version of XCE Engine.
Secondary Root
Contains the dom0 root file system for the previous version of XCE Engine.
Swap
512 MB
Swap space.
Log
Used to store log files.
Repository
Balance of
Volume Group
This volume uses most of the disk space. Used to store:
VHD files for all installed Virtual Machines (VMs)
VHD files for the Connect VM
Engine update kits downloaded from Synchronizer
Engine diagnostics and problem reports
*If the disk encryption option is chosen during Engine installation.

6. 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.

7. 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.

8. 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.

9. Engine Disk Sizing

10. How Many Bytes In a Gigabyte?
Disk Manufacturers
1 GB = 1,000,000,000 (109) bytes
Windows
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).

11. 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.

12. Disk Sizing Example
Engine
10 GB
Dock (enabled in Engine policy)
Windows XP VM (deployed from Synchronizer)
16 GB system disk (x2.0)
8 GB user disk (x1.5)
4 GB local disk
48 GB
Windows 7 VM (deployed from Synchronizer)
40 GB system disk (x2.0)
10 GB user disk (x1.5)
20 GB local disk
115 GB
Windows 2008 Server VM (local)
50 GB system disk
No user or local disk
50 GB
Subtotal
233 GB
Total (add 7%)
249 GB
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.

13. Encrypted Boot Sequence

14. 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).
Root Volume
Boot Volume
Repository
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.

15. Encryption Unlock Screen
Password:
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.
Root Volume
Boot Volume
Repository
Boot Volume Status
Unlocked.
Root Volume Status
Locked. The root volume cannot be unlocked until the user provides the password.
Repository Volume Status
Locked.

16. User Enters Unlock Password
mypassword
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
Repository
Root Volume
Boot Volume Status
Unlocked.
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.

17. 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
Root Volume
Repository
Boot Volume Status
Unlocked.
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.

18. 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
Root Volume
Repository
Boot Volume Status
Unlocked.
Root Volume Status
Repository Volume Status
Unlocked. This volume contains VHD files for VMs which can now be started.

19. Encryption Setup and Passwords

20. 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.

21. Password Validation After Encryption Unlock
Synchronizer
password
Engine AD
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.

22. 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.
New password is validated, password cache is updated, and encryption is setup with the new password.
The user is prompted to enter a new password.
Active Directory password validation fails. AD
password
INVALID
Or validation of a local password fails at the Synchronizer.
Synchronizer
Engine clears the password cache.
Engine
At the end of this process, the AD password, the Engine password cache, and the encryption unlock password are all synchronized.

23. 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.

24. 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.

25. 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.

26. 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.

27. 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.

28. Computer Storage Report

29. 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.

30. 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.

31. 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.

32. 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.

33. 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.

34. 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.

35. 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.

36. Summary Results
Current amount of free disk space available for new VMs or VM growth.
Total current size of all VHD files for all VMs.
Total extra space that would be used if all VHD files grew to maximum size.
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.

37. 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 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.
The VHD file for the local disk begins much smaller than the 30 GB logical size. VHD files start small and grow as required.
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.