Tuesday, January 28, 2014

How I learned to stop worrying (about power cuts) and love my Raspberry PI

As many other hobbyists I got myself a Raspberry PI a few months ago. It's very cool that such a functional piece of hardware can be so cheap. I'm using mine as a backup server for my photos, documents, videos etc, it is my Samba Server, FTP server and, most importantly an XBMC network server.

I'll outline some of the things that I did to make mine working the way I wanted to, but first I'd like to address the biggest issue that I experienced with my Raspberry PI: the fact that it doesn't deal well with power cuts. The PI itself isn't really to blame for that, its a general issue with Linux and other unix-type operating systems: sudden power losses can make their boot/os disk unreadable. With Linux running on a laptop you don't really have that issue, as your laptop has a built-in UPS, but my PI doesn't have that. Which means that I often happened to find my device in a state that it wouldn't boot up again. Apparently we had a power blip.
While some companies are starting to sell UPS solutions for the PI, one of the main issues with that is that the UPS often costs more than the PI itself. If you don't want to spend that extra money, I have used a different setup that gave me the capability to survive PI boot disk corruptions without too much work or cost.

Backup your PI boot SD card

Some people suggested that the best way to prevent your PI from corrupted boot disks is to make the disk readonly. While certainly a good idea, this doesn't really work for me as I often experiment with my PI and change its installed packages regularly. So I didn't want to restrict myself that much.
What I did instead was use Billw's cloning script to make a backup copy of the main SD card on a second one. I used an old SD card that I still had lying around and got a USB SD card adapter, which sells on ebay for about £1 including shipping. Using that script I make regular backups of my main SD card onto its clone. When experiencing one of those regular power blips and the PI doesn't want to start up, I simply swap the SD cards - the one from the USB goes into the main SD card port and vice-versa! That will allow me to start up the PI again with all my configuration as I had it. Then simply run Billw's script again to clone the SD card that's still working back on the corrupted one at which point I'll have two working SD cards again!
I've used this mechanism for a few months now and it works pretty well. Certainly much cheaper than a UPS and although a little bit of work (you need to ensure that the backup SD-card stays up-to-date) I found that it worked great. You can also automate the cloning so that it happens automatically every night or so...

In addition to the backup script there are a few other things that I tweaked for my PI. They might be a little different than what you're used to on Linux, so I'm outlining them here.

Get a Hard Disk with power-save

If you're planning to use your PI as a file server, like I do, get a USB harddrive that has a power-save feature. This means that you can have your system running 24/7 but that there won't be any spinning parts if nobody's using it, and very low power consumption too in that case. I got this Seagate 2TB one for about £60 which works great! The only thing you need to do is enable the power save feature once, which you have to do on a Windows PC using the program that comes on the drive. Once power-save enabled, you can connect it to the PI and it works perfectly. Note that you do need to sudo apt-get install ntfs-3g to use most pre-formatted USB drives.

Use UUIDs to mount your drives

Another issue that I was experiencing was that my USB drives didn't always get the same disk identifier after a PI reboot. One disk would sometimes be sdb and other times it would be sdc, for example. This is problematic if you use the standard 
  /dev/sda1 /disks/x1 auto noatime 0 0
in your /etc/fstab to mount your drives to a directory, as your mounted directory would sometimes be mounted to one disk and sometimes to the other...
A good solution to that is to mount your drives by UUID instead. If you look in /dev/disk/by-uuid/ you can see the UUIDs of all the available disks. Find the right one and use that to mount your disk. The following makes sure that always the same disk is mounted to /disks/x1:
  /dev/disk/by-uuid/5A22DB2D2DB0CBF /disks/x1 auto noatime 0 0

Rotate the logs

If you're doing a lot of file transfer to-from your PI, the Samba/FTP log files can get pretty big. If you, like me, use a crappy old 4GB SD card to run off, it might make sense to keep the size of the log files down. Logrotate allows you to do this, and the standard Raspbian distribution comes with this installed. I just tweaked it to keep the log files smaller, by only remembering 1 week of logs. To do this, you tweak /etc/logrotate.conf, I'm using these settings:
  # rotate log files weekly
  weekly

  # keep 1 weeks worth of backlogs
  rotate 1

  # create new (empty) log files after rotating old ones
  create

  # compress log files
  compress


Serve XBMC throughout the house

Many people use the PI to run XBMC directly. XBMC is a wonderful media playback application that gives you a really nice interface to your media collection. And a PI connected to an audio/video system can certainly be used for running it. However, I was looking for something different. I wanted to use my video library on any device in the house. Maybe a laptop, maybe our multimedia pc which is connected to the tv, maybe even on an Android smartphone. XBMC has features that allow you to do this. To get this working, you don't actually need XBMC on the Raspberry PI at all! You need the video files on it, a network file access protocol, such as Samba, and an installation of MySQL which is what the XBMC installations on the client computers communicate with to show your video library etc. The whole setup is really nice as it allows you to watch your videos on any device in the house and it even remembers where you left off if you stopped halfway, so that you can easily continue watching on another computer. Once you've installed Samba and MySQL for XBMC on the PI, you need to install XBMC on all the client devices that you want to use. There are builds available for most platforms. Next you need to configure XBMC to use MySQL. I actually use different profiles to organize my video files, for example you may have holiday videos in one and educational videos in another profile (or any other separation of your choice ;). You can do this by putting the advancedsettings.xml file in the .../userdata/profile/<Profile Name> directory and name the database in it to separate the content, like this:
  <advancedsettings>
    <videodatabase>
      <type>mysql</type>
      <host>my_pi_host</host>
      <port>3306</port>
      <user>mysql_username</user>
      <pass>mysql_password</pass>
      <name>my_holiday_movies</name>
    </videodatabase>
  </advancedsettings>
The name tag in the configuration is used to connect to separate MySQL databases running in the same database server. That allows you to serve different media depending on the XBMC profile you're in. In the Holidays profile it lists my holiday videos, in the Education profile it has my educational ones.

Finally, when you add videos to your database, make sure to select add the directory on the PI using a network protocol that works on all your devices. For example a Samba URL: 
  smb://my_pi_host/share/holiday/videos/
And voilĂ , you will get all your movies on all your XBMC devices.

Ok, so this was a random collection of bits and pieces that I did to get my Raspberry PI to do what I wanted. If you have a nugget of PI goodness, leave a comment to share :)

3 comments:

Seweryn Niemiec said...

"its a general issue with Linux and other unix-type operating systems: sudden power losses can make their boot/os disk unreadable" - this is FUD.

I'm using Linux for about 18 years, on computers from workstations, by standalone servers, to blade clusters and I can't remember any single failure like this.

David Bosschaert said...

@Seweryn
I don't think the corrupted boot disk on system crash is purely a PI issue. I do agree that it happens less on desktop unix systems (although I have seen cases like this on Linux and Solaris). Maybe the desktop systems are better prepared for it and maybe it's less of an issue with disk drives compared to sd cards. In any case the PI suffers pretty badly from this...

BTW See here http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=36533 for some more tips on preventing SD card corruption.

Mazya uchapati (my low-tech efforts) said...

Hi David,

It's a nice round up of your experience. I had Raspberry pi from last year and played a bit with XBMC earlier and then just sitting idle. I was thinking of the same usage for my NAS backup and it's good that I can use your experience to make sure I have stable system like you.