How I backup LVM volumes on my Xen server

I’ve got a Xen server which runs a couple of Linux and Windows VMs. The VMs are stored in LVM volumes on a LVM volume group which is on a bcache device. The bcache device consists of a mirrored SSD pair (using mdraid) as cache and a mirrored HDD pair (also using mdraid) as backing storage. The SSD caching gives a nice performance boost, but nowadays I would go with SSD storage only, because bcache caused some problems (did not play nice with udev during boot).
The Windows VMs are backed up by installing the UrBackup client in the VMs. To restore I’d need to boot the restore CD in Xen or restore the Windows images via command line in the hypervisor.
The Linux VMs are backed up at hypervisor level in the Xen dom0 (which is Debian in this case) using LVM snapshots. To create and remove LVM snapshots I have following snapshot creation and removal script (the volume group on which the volumes are is mirror-vg).

Snapshot creation script at /usr/local/etc/urbackup/create_filesystem_snapshot:

set -e
if [[ $VOLNAME == "" ]]; then
        echo "No volume name specified"
        exit 1
if [[ $VOLNAME == "other-data" ]]; then
if [[ $SNAP_UID == "" ]]; then
        echo "No snapshot uid specified"
        exit 1
lvcreate -l100%FREE -s -n $SNAP_UID /dev/$VGNAME/$VOLNAME
trap 'test $SUCCESS = 1 || lvremove -f /dev/$VGNAME/$SNAP_UID' EXIT
mkdir -p /mnt/urbackup_snaps/${SNAP_UID}
mount -o ro /dev/$VGNAME/$SNAP_UID /mnt/urbackup_snaps/${SNAP_UID}
echo "SNAPSHOT=/mnt/urbackup_snaps/$SNAP_UID"
exit 0

Snapshot removal script at /usr/local/etc/urbackup/remove_filesystem_snapshot:

set -e
if [[ $SNAP_UID == "" ]]; then
        echo "No snapshot uid specified"
        exit 1
if [[ "$SNAP_MOUNTPOINT" == "" ]]; then
        echo "Snapshot mountpoint is empty"
        exit 1
if ! test -e $SNAP_MOUNTPOINT; then
        echo "Snapshot at $SNAP_MOUNTPOINT was already removed"
        exit 0
if ! df -T -P | egrep "${SNAP_MOUNTPOINT}\$" > /dev/null 2>&1; then
        echo "Snapshot is not mounted. Already removed"
        rmdir "${SNAP_MOUNTPOINT}"
        exit 0
if lsblk -r --output "NAME,MOUNTPOINT" --paths > /dev/null 2>&1; then
        VOLNAME=`lsblk -r --output "NAME,MOUNTPOINT" --paths | egrep " ${SNAP_MOUNTPOINT}\$" | head -n 1 | tr -s " " | cut -d" " -f1`
        VOLNAME=`lsblk -r --output "NAME,MOUNTPOINT" | egrep " ${SNAP_MOUNTPOINT}\$" | head -n 1 | tr -s " " | cut -d" " -f1`
if [ "x$VOLNAME" = x ]; then
    echo "Could not find LVM volume for mountpoint ${SNAP_MOUNTPOINT}"
    exit 1
if [ ! -e "$VOLNAME" ]; then
    echo "LVM volume for mountpoint ${SNAP_MOUNTPOINT} does not exist"
    exit 1
echo "Unmounting $VOLNAME at /mnt/urbackup_snaps/${SNAP_UID}..."
if ! umount /mnt/urbackup_snaps/${SNAP_UID}; then
        sleep 10
        umount /mnt/urbackup_snaps/${SNAP_UID}
echo "Destroying LVM snapshot $VOLNAME..."
lvremove -f "$VOLNAME"

The snapshot scripts are specified via the file /usr/local/etc/urbackup/snapshot.cfg:


Then I have a virtual client for each LVM volume that needs to be backed up. I have put those virtual clients in a settings group with the default path to backup “/|root/require_snapshot”.

For restore I need to recreate the LVM volume. Create a file system on it (e.g. with mkfs.ext4) mount it in the hypervisor and then restore via.

urbackupclientctl restore-start --virtual-client VOLUMENAME -b last –map-from / --map-to /mnt/localmountpoint

Windows Backup API support in UrBackup 2.1.x

UrBackup 2.1.x has more completselect_windows_componentse Windows Backup API support. Previously the backup API was only used to create snapshots of the specified paths to backup (volume shadow copy snapshots). Now it does a so called component level backup, if configured to do so. You can select the components to backup via the client user interface and then the selected components automatically communicate to UrBackup which files need to be backed up, and on restore it communicates where the files should be restored and if e.g. services should be restarted during/after restore.select_restore_components

This works with applications which in turn support the Windows Backup API, such as for example Microsoft Exchange, Microsoft SQL Server, Microsoft Hyper-V, Oracle DB on Windows.

Testing backup and resrestore_componentstore with those different applications is now the big item on the to-do list. Every help and pointers to applications where backup or restore is broken will be helpful.

Visual Studio 2015 runtime and MSI installer

If you are using the MSI installer to install either UrBackup Client or Server on Windows there is a potential problem you might run into.

Starting with Visual Studio 2015, with which UrBackup Client/Server 2.x are compiled, Microsoft decided to split the Visual Studio runtime into a operating system level component (Universal Runtime) and another “normal” runtime component, wheras earlier it was only a “normal” runtime component.
The operating system component is installed via Windows Update and cannot be installed by a MSI installer. With Windows 10 it is always installed, but with Windows Vista or 8.1 the system needs to be up to date in order for the system component to be present (KB2999226), otherwise UrBackup will not start.

Another work-around is to use the .EXE (NSIS) Installer which includes the operating system compontent. Installation depends on Windows Update functioning correctly (which it may not).

Let’s just say this change does not make the software developer’s and user’s life easier.

New in UrBackup 2.0.x

Wactivitieseb interface modernization. The web interface was a little bit utilitarian which gave many people the wrong impression. With the help of mombojuice the web interface was improved such that it looks much more modern and professional. Many small improvements were made as well. For example the dates are now formatted according to browser locale, backups can be started via drop-down menu and the live log of a running backup can be directly accessed from the activities screen.

Improved file deduplication. Completely reworked the file deduplication and file backup statistics calculation. This should be much faster, scalable and reliable now.

File lastmodifiedbackup improvements. File meta-data such as last modified time and file permissions are now backed up on all supported client systems (Windows, Linux, Mac OS X). Supporting more exotic file system features such as sparse files UrBackup is now a fully featured file backup solution.

File backup restore. To restore the file meta-data UrBackup has now an integrated file restore. The file restore reuses client-side hashes, if present, and transfers only differences, such that restoring folders with only few changes since the restored backup is fast.

access_backupsDirect backup access. If configured, the backed up file permissions are used to allow clients direct access to their files with only minimal configuration. On Windows there is a shortcut in Explorer which directly opens the relevant/file folder in the browser. There is a new list view which shows a file/folder in all backups. For files, hashes are used to show when the file content changed (versions).

image_backup_settingsImage backup improvements. UrBackup supports GPT formatted disks now and the restore CD boots on UEFI firmware devices (also with secure boot enabled). In combination with btrfs, UrBackup supports an incremental forever style image backup and image backups over 2TB. For VHD/VHDZ UrBackup has now settings to base incremental backups on the last or last full image backup. Full image backups can be configured to be synthetic full backups transferring only changes since the last image backup.

Significant security improvements. Forward secrecy for Internet clients via ECDH and Internet client security improvement by using AES-GCM. Switch from DSA to ECDSA for client update and server identity signatures. Web server/restore CD login now uses PBKDF2.

Mac OS X client. There is nowmac_backup_running a UrBackup Client for Mac OS X. This client is fully featured, excluding image backup (like Linux client). The Mac OS X client can be used as a technically superior backup solution to Time Machine.

Improved command line. Mainlttyy for Linux all command line usage has been significantly improved. This includes the command line client (urbackupclientctl), the server command line (urbackupsrv) and the restore client.

Linux file system snapshotting. Snapshotting now also works on Linux and is fully integrated. A portable Linux client includes snapshot scripts for LVM, dattobd and btrfs which work without changes in most cases.

Lots of other changes. Proper symbolic link backup. Virtual clients allow you to backup different sets of files at different intervals and max/min amounts. Simultaneous image and file backups. Different backup speeds and backup intervals at different times. Improved Internet transfer compression. New hashing method where the server only needs to hash changed parts of a file.


Start of UrBackup 2.0 beta phase

UrBackup Server/Client/Restore 2.0.0 beta was recently released. This marks the beginning of the UrBackup 2.0 beta phase.

See the forums for download links and discussion.

UrBackup 2.0 marks the beginning of UrBackup having no major limitations. If you still find some please start a discussion in the forums. The next beta version will also properly support sparse file backup.

Progress update on the next major UrBackup version

Currently the next major UrBackup version is kind of close to getting finished. There are a few major work in progress areas. Once they are finished and I have done some overall testing I will release a beta version.

The major changes in the new version are:

  • Completely reworked the file deduplication and file backup statistics calculation. This should be much faster, scalable and reliable now.
  • The Copy-on-Write image backups on btrfs mentioned in the last post. Synthetic full backups for the VHD/VHDZ file format and settings for basing image backups on the last full or last incremental backup (differential/incremental).
  • File backups include file metadata including file modification time, ACLs, alternate data streams etc.
  • Backup of streaming data. E.g. the output of “mysqldump”/”pg_dump”. I plan to add basic backup scripts for popular Open Source databases to the client
  • New file restore feature which restores file backups and properly restores the file meta-data
  • The ACLs/file permissions are used to enable users to directly access backups on the web interface from the explorer on the clients (via right click -> Access/Restore backups)
  • Proper backups of symbolic links. Symbolic links which point to folders/files which are backed up are backed up as symbolic links and symbolic links which point outside of the selected backup set are followed/not followed depending on a setting
  • The web interface has been bootstrapified ( – mombojuice did the work) and looks much more modern now
  • Simultaneous image and file backups
  • Backup and restore EFI boot sector and partition on UEFI systems. Restore CD that boots with UEFI firmware
  • Client for Mac OS X
  • Forward secrecy for Internet clients via ECDH and Internet client security improvement by using AES-GCM
  • Switch from DSA to ECDSA for client update and server identity signatures

Still to do:

  • Lot’s of testing and bug fixing
  • Backup and restore of file meta-data on Mac OS X and Linux
  • Symbolic link backup handling on Mac OS X and Linux
  • Automatic client update for Mac OS X like for Windows
  • Restoring files which are in use on Windows (via restarting)
  • Update Documentation

Remaining UrBackup limitations (to be done after with a subsequent version):

  • Recognize hard links and backup the files only once
  • Backup only used areas of sparse files
  • Continuous file backup

Once the “to do”s are done this is a big step forward for UrBackup. Having streaming file backups and incremental, differential, synthetic full and full image backups basically allows you to implement pretty much every backup strategy with UrBackup. The only thing missing is the continuous file backup and I already started work on that.

For example you could use UrBackup instead of TimeMachine on Mac OS X and do a full system restore via the file restore feature (this is not implemented at all – it is just an example what it might be able to do). You probably don’t even need an image of your Windows system partition but can restore it via the file backup restore (albeit inefficiently, because the hard links in C:\windows\winsxs are not handled properly).

Status of next major version

I’m releasing UrBackup Server 0.26.1 and Client 0.40.1 soon. They do have only minor bug fixes and additionally a Russian translation.

The next major version, which will probably be 1.0, will have following new features:

First of all you will be able to start and stop backups from the server web interface.


Then I reorganized the settings, both on the server web interface and on the client. You can also see the new bandwidth throttling feature which can limit the bandwidth usage of the backup server, both globally and for each client.


I added a few features to the new internet mode, described in the last post. Per default UrBackup does not do full file backups or image backups with an internet connection, but it can be enabled. Total global backup speed and backup speeds for each client can be set separately from the local backup speed. You can e.g. use this on the client to prevent UrBackup from using all your bandwidth. Additionally to being able to encrypt the transfer over internet UrBackup can now also compress it.




There is a new feature which lets you archive certain backups in certain intervals. Archived backups are not deleted during cleanups, until they are not archived anymore. Additionally to the automated archival you can also manually archive and un-archive certain file backups simply by clicking on them. For now only file backups can be archived.


This should be the major improvements. The are some minor ones as well.

Everything except the internet mode is ready for testing, so if anyone wants to help send me a mail at or drop by in the forums and I will upload the appropriate builds.

Internet Mode

Currently I’m working on a new internet mode for UrBackup. This means that you will be able to backup clients to a server on the internet with the upcoming new version.
This communication is of course encrypted and authenticated. It uses a shared key encryption with AES256 in CFB mode. It should be easy to configure: You just need to supply the server with its internet name/IP and the ports the clients should connect to. These settings, as well as random keys, are then pushed to the clients via the local (trusted) network. They can be manually entered on the client side as well. Then the key is pushed from the client to the server.

If you are not in the local network the client tries to connect to the internet server, if you entered something (e.g. a dns name or IP address) there. Then both check if they have the same key and if they do have the same shared key a normal connection, like if the client were in the local network, is established and backups can be performed.

I’ll now implement special options for disabling image and full file backups for clients connected via internet. Then I will implement a special, block based file (rsync like) transfer mode which will be used for those clients and which transfers less data in some scenarios.

Then you can look forward to backup archival and more detailed backup retention capabilities, which I’ll be working on next.

Desktop GNU/Linux: You Have to Love It

You know those parents that love their child so much, they do not see how bad their child in reality really is. I think you have to have a similar relationship to GNU/Linux if you really want to use it as your desktop operating system. That does not mean, that it is generally bad. Just like the child it has its strong points. E.g. the kernel. I am an avid fan of Linus Torvals autocratic management of kernel development. And have no doubt, it is autocratic. He decides in which direction the kernel moves and the success the kernel has had, is in my opinion, largely caused by his pragmatic style.
One could say that the success of the kernel part of GNU/Linux was caused by his strong leadership. And in areas where the operating system does less well, there is a lack of leadership.
For example the window managers. Mainly there is KDE and Gnome. They have different UI frameworks and it is already kind of sacrilegious to use a KDE application in Gnome, because it uses more memory. But additionally to that, this application won’t have the same style.
Of course they have different systems for start menu entries, tray icons, settings and pretty much everything you can think of. Thankfully there is kind of a standardization body named The problem – as with every standardization process – is that it moves slowly and the resulting standard does not define all useful scenarios. Thus the new features are sometimes still not accessible in a common way.
We speak here of a fragmentation within the operating system: In order to make a GNU/Linux application which uses UI and has a native look&fell you need to do everything twice now. Once with GTK and once with Qt (used by KDE).
But this does not end there: You have to think of the zillion other window managers out there. XFCE, Unity, Fluxbox you name them. Thankfully most are based on either GTK or Qt. Nevertheless: In each one of those, your application may not display its tray icon correctly.
And as you perhaps know: The UrBackup Client displays a tray icon.

Anticipating all these complications I am using a cross platform toolkit for the UrBackup Client: wxWidgets. Theoretically it is available for both Qt and GTK. As every level of abstraction this gives you slightly less power, but the application is simple right?
Well, try to show such a balloon popup on windows and we can talk. But otherwise it really worked mostly well.
So I compiled the client in Debian and checked if everything was working. And it did. Then – to test it in a more popular desktop distribution – I downloaded Ubuntu.
The tray icon did not show up. Turns out Unity has a whitelist of apps that can show tray icons. This annoys many users as e.g. Skype won’t show up any more. You can of course allow tray icons by editing some arcane setting somewhere. But this is not something the end-user should do right?
But it gets worse: After I edited that setting to allow all applications, it still did not work.
Turns out they did not like the standard any more and made their own. In order for it to work I would have to use a separate library (libappindicator) to display the tray icon. Libappindicator only works with Unity on Ubuntu, so I would have to make and release a different version of my application for Ubuntu. Not acceptable.
I’ll repeat: I’m using libwxgtk2.8 which is officially part of Ubuntu to display a tray icon. This does not work because wxWidgets uses the protocol to display the tray icon which Ubuntu decided to abandon. The wxWidget guys (understandably) seem to not want to fix that issue in wxWidgets 2.9, probability because they do not want to implement something only for Ubuntu, as well.
Simultaneously the Ubuntu fork Mint which does not use Unity is becoming more popular. So perhaps this specific problem will resolve itself this way. This issue certainly seems to have caused some waves:
Bottom line of that article is that the standardization process is broken. And this is just one example of the kind of fragmentation we developers have to think about.
Compare that to Windows where the program that displayed tray icons in Windows 95 probably still can display it in Windows 7. After 11 years! Too easy.

I said at the beginning that a strong leadership is needed just like for the Linux kernel. This strong leadership would have to coordinate efforts in different window managers and in different distributions. This is difficult because the distribution is the thing the users sees and holds responsible for something that is not working. This is also the reason why you install packets from your distribution. Because doing it any other way probably causes something to not work or even break. Because only distributors are accountable it is very difficult to establish something like – an inter distribution standardization body. There is simply no incentive to play along nicely, especially since standardization processes tend to be lengthy and difficult and you want your distribution to be progressive and modern.
The only way I see this dilemma could be solved, is by having one distribution which the majority of GNU/Linux (desktop) users use. I hoped this could be Ubuntu lead by Mark Shuttleworth. But Ubuntu is sadly moving into the wrong direction at the moment.
Additionally to that. It is moving too fast. Given some time and persuasion Gnome probability would have adapted the libappindicator interface and I would not have this problem now.
Unity is – in my opinion – really crappy. I did not even find out how to switch applications without alt+tabbing and had to use the windows key to start one (start menu where are you?). If this is someone’s idea of usability and end user friendliness then I give up all remaining hope for Ubuntu.

Given all that, I have decided to not start building any packages for Ubuntu/Debian. The support matrix would just be too great and I already named one issue. If you really love Linux that much that you use it as a desktop operating system, I leave you to grab the source code and build it yourself – no guarantees that it works on your specific distribution in your window manager. Thankfully the back-end part – the part that does the backups – is not dependant on any flaky UI/Window manager stuff and so should be there to stay. If the frontend does not work for you (aka it does not display the tray icon) you can always set the directories it backs up on the server.
I hope that some time in the future someone from a distribution picks up that code and builds working packages for that distribution. But that someone won’t be me. This far, and no further! Sorry, Linux. I will still love you. But only as my server child. Not a desktop one.

MSI installers with next version

I finally bit the bullet and worked on MSI installers for Windows. As anticipated it was not easy. I used WiX.

They do have some advantages over an installer distributed as “exe”:

  • One can add the Microsoft Visual Studio runtime as a “merge module” thus avoiding starting it in the installer manually
  • Apparently installing centralized on domain computers is easier

On the negative side:

  • No shared 32/64 bit MSIs are possible. That means the user has to select the right one before downloading
  • You cannot add custom commands as easily as in NSIS

I think I will only publish 64bit MSIs for now. Most Windows Servers should be 64bit now anyway and I will still publish the “old” installers for users of older and 32bit systems.