Sugar Labs @ NDSU

Building a smarter computing culture in Fargo, ND

Is SoaS ready for prime time?

We’ve been using Sugar on a Stick (SoaS) for almost two years now in after school programs, and generally its performance has been acceptable.  I wouldn’t want to be a classroom teachers with 20+ kids trying to make it work, but 12 kids in an after school program is doable. When a stick fails, we  just swap it out and give the student a new one.  Occasionally, a student would get two that failed, and become frustrated, but in a 45 minute session, that isn’t the end of the world.

Today, we had so many failures we lost track.  We only had 10 kids, 6 sticks working (at least initially), and eventually 8 worked with two kids doubling up.  We also had to break out 2 laptops because part of the failure seems to be related to the desktops we are using, but even the success-fail rates with the desktops are totally random.  Computers that worked fine last week didn’t work this week.  Computers that did not work last week did work this week.  I suppose the logical thing to do in order to track success and fail rates is to put the same sticks in the same computers every week.

I am just wondering who is using SoaS on a regular basis in a school or after school setting, is it similarly problematic in other settings, or are we doing something wrong with our imaging of sticks?


14 comments on “Is SoaS ready for prime time?

  1. Peter
    May 1, 2012

    As the maintainer of SoaS I can say it’s relatively stable installed on devices but then I’m not a kid and I know they use it in a whole lot of ways that I as a developer don’t. I do know that USB keys aren’t always stable and that applies especially the cheap ones and they get worse with more writes.

    SoaS isn’t perfect but I also get very little feedback from people that are actually using it and it would be nice if you came and participated on the SoaS mailing list so that I was aware of the issues you’re seeing rather than drive by blog posts.

  2. codewiz
    May 1, 2012

    Peter, I believe they’re hitting that longstanding problem with the dmraid overlay running out of free blocks and corrupting the ext filesystem as a result.

    If the problem occurs after writing a lot of data to the journal, then it’s definitely this problem. There’s a very simple technical solution, but currently it’s not easy to perform for end-users.

    • Peter
      May 2, 2012

      The issue with easily creating live USB sticks without the overlay is being worked upon, as usual it never moves as fast as I would like and unfortunately I have to rely upon others for getting it done as it’s out of my skill set. I’m hoping we might have a solution in the Fedora 18 timeframe.

  3. tgilliard
    May 1, 2012

    use “liveinst” from sugar-terminal (su). This will do a real install of Sugar-on-a Stick.
    use “custom” and format the 4 GB USB or larger (8 GB is better):
    gpt 2 ; /boot ext4 500; / ext4 balance of the USB. No swap.

    This is a real install using the USB as a Hard Disk install. No persistent failures.

  4. kab13
    May 1, 2012

    Agreed, SoaS is generally stable but wasn’t today and wouldn’t be stable enough for a k-12 teacher based on our experiences the last two years. We are interested in working out the bugs and getting a stable enough for the K-12 setting; I’ll have our technical people look at these responses. SoaS list doesn’t speak my language, which is “Minimally-technical.” : )

    Related topic; regardless of the instructions we provide, very few kids are able to get SoaS to work at home. We suggest F2, F11, F12 and Esc to get to boot menu. We show them how to do it at school and they have no problems. We spent a lot of time on Virtual Box solutions but those don’t work well in school settings nor at home. Requires more RAM than schools and home computers have available. Windows hogs too much. We are working with families whose computers are older, underpowered, kids often the computer experts at home. Schools won’t install Virtual Box on machines: don’t have the tech support to take on special projects like this.

    Thanks for taking the time to respond.

    • Peter
      May 2, 2012

      SoaS list is fine if you’re “minimally technical” for non technical feedback or your tech people could subscribe instead 🙂

      As for getting it to work at home, unfortunately it is quite technical and generally harder than it should be to get a device to boot from USB. It would be of interest to me if it would be possible to do a poll of what sort of machines the kids have at home (make/model) and we might be able to do a “boot support matrix” ie If you have Make X do Y sort of thing. Mac’s for example should have drastically improved boot support in SoaSv7 but I don’t have one to test.

      As for VirtualBox…. it’s never a solution IMO and that why SoaS doesn’t support it officially. 1) the kids works isn’t portable 2) each kid has to have a differnet VM on the same machine each week etc.

  5. Davin
    May 1, 2012

    Hello I make the sticks for our group, after reading a few responses here it’d be good to get in a few words for constructive progress. We use the Live Disk to drive command, and we use 4GB sticks 1GB is allocated to the home directory (which is unencrypted as well) 512 MB is allocated to the overlay. I usually partition the sticks with one ext 4 formatted partition taking all of the available space.

    “Peter, I believe they’re hitting that longstanding problem with the dmraid overlay running out of free blocks and corrupting the ext filesystem as a result.”

    How long would it take for 512 MB overlay to fill up? During my tests I found journal writing to be an issue which is why I made the home and overlay a little bigger than the recommended settings I’ve used a stick for upwards of 2 hours before without any problem. It might just be that I’m not doing enough or changing activities frequently to break it. I feel like they’re stable but as you said Peter the kids are probably using it completely different then the way I’ve tested them.

    • codewiz
      May 1, 2012

      > How long would it take for 512 MB overlay to fill up?

      Children download things, make videos and try all activities… until the filesystem becomes full. But before then, the overlay will run out of free blocks. At this point, dmraid will tell ext4 that writes are failing, and the filesystem will be remounted read-only.

      To the user, this situation will look like the system has crashed; eventually, they will reboot. On the next boot, the system will notice that it’s in an unclean state, and will try to replay the pending transactions in the ext4 journal (not to be confused with Sugar’s Journal). Unfortunately, the overlay device is still 100% used, causing the journal replay to fail.

      You can verify my theory by downloading (or creating) a file larger than 512MB. If I’m right, the USB stick will corrupt *systematically* every time you repeat the test. This is different from the (much rarer) corruption due to normal flash wearing.

      The best way to solve this issue is to get rid of the extra complexity of an ext4 partition split between two devices (a compressed file and an overlay). This layout evolved out of the Live CD which was read-only media, but there’s no technical reason for using this layout on a USB stick (which looks just like a regular hard drive, except it’s smaller and slower).

    • Peter
      May 2, 2012

      If your using a separate 1Gb home directory it shouldn’t be using the overlay at all. The overlay is used for the core OS for things like changes to /etc /usr. Things like journal and video should be on the 1Gb home image and I would have thought it would take a little while for kids to fill up 1Gb unless they’re doing a lot of video. Would be great if you could pop over to the SoaS list and spend a little of your time to see if we can work out what’s going on, or drop me a mail directly.

  6. Davin
    May 2, 2012

    Thanks I noticed it would fail updates for the sticks if I don’t use the overlay. I can’t do a full system update without larger overlays but then I worry about other data storage since we’re only using 4 GB drives, and with the 512 MB overlay I am able to update activities without errors so I’ve left it at that.

    I’m trying to arrange my schedule to go to the event with the students so I can see if I can find anything I can improve or why they fail. Wish I could have done it earlier but it’s just the way it turned out. I’ll report anything that might help.

    • Peter
      May 2, 2012

      Ulimately liveusb sticks aren’t designed to be “yum updated” like standard installs, the idea more is that you re-flash the sticks with a newer build of the live image. The overlays aren’t meant to have large amount of change delta but rather are designed to allow persistent data to be saved such as wifi details.

    • fgrose
      May 3, 2012

      You can query the overlay consumption with the command,
      dmsetup status

      See for more background and other ideas.

  7. tgilliard
    May 2, 2012

    For the more adventurous, this makes a longer lasting; persistent USB:

    sudo ./ –reset-mbr –overlay-size-mb 500 –home-size-mb 900 –delete-home –unencrypted-home Fedora-17-TC2-i686-Live-SoaS.iso /dev/sd(x)1


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This entry was posted on May 1, 2012 by in fieldnote, Sugar.


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