Btrfs: Experimental or approaching stable?

Thinking that btrfs should approach a stable status by now, I used it as file system for the backups on my primary test server. Well, it works well and is really fast. Compression seems to work, too.
But there was a unexpected warning during one backup. It could not create a hard link. In this case UrBackup logs a warning and copies the file.
I checked the inode number of the file that failed to link and it was hard linked nonetheless – weird: Btrfs claimed it could not hard link even though it already did it. There were also only about 500 links to that inode. I checked the file system limit for the number of hard links and discovered that btrfs supports as few as 31 hard links to the same inode in one directory.
There is a relatively new patch to raise this limitation http://lwn.net/Articles/498226/, but it has not landed in the kernel yet. This issue does not affect UrBackup that much, but nonetheless, it shows us something about the stability of btrfs.
Thus my advise: Don’t use it yet.

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 martin@urbackup.org 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.

I’m better than you, Explorer

A long time ago I fixed a bug, where UrBackup Server on Windows could not backup files with a path name longer than 255 characters. It’s here:
https://sourceforge.net/apps/mantisbt/urbackup/view.php?id=2
Yesterday I reinstalled a test server and today I wanted to delete the old UrBackup backup folder. It threw error messages like you see in the screenshot.
Apparently the Windows Explorer (even in Windows Server 2008R2) cannot delete files with path names longer than 255 characters. And contrary to the error message you can also not move or rename them. You have to install some alternative file manager, to get rid of these files or shorten directory names such that the path length is smaller than 256 characters. Or let UrBackup delete them. In my case: I just left the folder there. I do not care. It’s a test server anyway.

Well done, Explorer.

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 FreeDesktop.org. 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 FreeDesktop.org 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 FreeDesktop.org 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: http://blogs.gnome.org/bolsh/2011/03/11/lessons-learned/
Bottom line of that article is that the FreeDesktop.org 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 FreeDesktop.org – 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.

No BerkeleyDB backend

My previous announcement that there will be a Berkeley DB backend was too hasty. I ran into some (for now) unsolvable problems. I posted them into the official Oracle forums but seem to get no reply there:
https://forums.oracle.com/forums/thread.jspa?threadID=2307258&tstart=15

The final nail in the coffin was, that the advertised increased concurrency was not present. In my tests it performed even worse then SQLite in WAL journal mode. That and the perceived instability (I had a database corruption once) shine a pretty bad light on Berkeley DB. Maybe the SQL layer for Berkeley DB which I used is not stable yet?

On the plus side the tables I had to denormalize cause a significant speed increase for SQLite as well, so all this work was not for nothing.
Maybe I will revisit Berkeley DB in a few months/years.

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.

Optional BerkeleyDB database backend

In the upcoming version of UrBackup Server you will be able to choose BerkeleyDB as database backend instead of SQLite. I am still deliberating about if I will make it the default in Windows. Not in Linux though as the BerkeleyDB version UrBackup needs is not yet e.g. in Debian stable.

The advantage of BerkeleyDB over SQLite is that it is build for higher concurrency. So if you want to have a lot of simultaneous backups you should definitely use it. The new SQLite compatibility layer of BerkeleyDB also made it very easy to add that alternative backend. (The BerkeleyDB people do not like you calling it a backend. They say it is a SQLite frontend for BerkeleyDB.)
It is not as robust as SQLite though. For example it has some problems when the filesystem the database is saved on is at its capacity limit. In my case it slowed down to a crawl. Also if you do not adjust the database parameters correctly it may throw “out of memory” errors. I am still testing what the correct parameters are. If you just set them really high it needs a lot of memory.
For example it said “Lock table out of lock entries” but increasing the number of lockers such that this error did not occur any more resulted in 1GB more memory usage. This is simply too much. I then tracked the problem down to a table join in which BerkeleyDB seems to need a disproportionately large number of locks. Denormalizing a table, such that this join is no longer necessary solved that problem, I think.
BerkeleyDB may also be slower in situations where no concurrency is involved as it has a much more fine grained locking system and in such situations then locks to much. So using it with only a few clients will cause unnecessary locking overhead.

I plan on automatically converting the database as soon as the BerkeleyDB plugin is loaded into UrBackup Server. So the only inconvenience should be a long database reconstruction time during which the database is converted.
The table denormalization and some index rebuilding will also take place on upgrade. This also took a lot of time on my test system.
Once you switched, converting back will be a manual job. I think I’ll have to write in detail about that once the new version is released.

Latest multiple volumes image backup feature and why you should not use it

I recently added a setting to configure which volume(s) UrBackup should backup as image. I added this because it was requested in the forums. Feature requests work! Try them as well!

I will now continue on to modifying the restore CD to allow one to select the volume to restore. This will not be much work, so expect it soon with UrBackup Client 0.39, Server 0.25 and Restore CD 0.3.

Nevertheless I felt a little bit uneasy while adding this feature, because it is not really necessary in my opinion.

Incremental file backups are usually really fast. Incremental image backups currently not so much. So you should use file backups whenever possible. As additional benefit restoring only part of the data is much easier with file backups than with image backups, where you have to mount the image. If you want to be able to do a bare metal restore though and you use Windows having an image backup of your system volume is unavoidable. Restoring from files is not possible without reinstalling.

I will talk about why you do not need image backups at all if you use Linux soon.

So because file backups are faster and more convenient and you only need an image backup of your system volume backing up any other volume as image backup is suboptimal.

But now UrBackup does not stop you from doing it. It is your choice now.

Bare metal restore for Windows Server 2008 R2 now working

A few days ago while I was testing the Image capability of UrBackup on XenServer (another story) I noticed that Windows Server 2008 R2 creates a 100MB large Partition called “System Reserved”. On closer look a partition like this also exists on my Windows 7 (x64). Windows 7 apparently keeps some files for booting there so that it can still repair the main C: partition in case something happens to it.
One user already mentioned that such a partition exists and UrBackup should also include it into the image backups, but I couldn’t reproduce the problem till now (I asked him which Windows he was using and he didn’t answer).
In order for the partition to not be created and used you have to manually partition during the Windows setup.

As this is a major bug/limitation of UrBackup, because it causes the restored images of operating systems with this partition not to be bootable I decided to fix this problem in Server 0.24/Client 0.38 (further delaying said versions). If this partition exists it gets downloaded to the server and is associated with the normal image backup of the “C” partition. If you restore an image the “System Reserved” partition will be restored after the “C” partition, if it exists on the server thus making a restored image of the operating systems mentioned above bootable.