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Thread: 13.1 : dual boot, btrfs and root partition

  1. #1
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    Default 13.1 : dual boot, btrfs and root partition

    Hi there,

    I just installed the 13.1 version, seems great !

    But I encountered a trouble at installation. I found a workaround, so no big deal, but still, I'd like to have some explanation, if someone can give it to me.

    I have a pc, x64, with 2 hard drives, and a dual boot with windows 8.1. My linux hard drive has a / partition and a /home one (besides the swap). I usually install grub on the root partition, and handle the dual boot with EasyBCD.

    I read in the release notes that although btrfs wasn't the default filesystem, it was deemed suitable for everyday use, and as I was doing a neat install, I wanted to give btrfs a shot.
    So I installed OpenSUSE ticking the "use btrfs as the default file system" box (the log screen shows a handful of subvolumes are created), edited the partition to mount and format / and /home, edited the bootloader to set it on the root partition (and not the MBR).
    The install went fine, but upon rebooting, I end up with the "grub>" command. I tried "ls", it showed something really close to my windows partition.

    After a few attempts, I tried the same thing, but setting my / partition as ext4 (leaving the /home one as btrfs). And guess what ? It worked !
    So I have now a functional system, with a btrfs home partition, and an ext4 / partition.

    Any ideas as what I should do to have both on btrfs ?

    Thanks a lot, and congrats to the OpenSUSE team !
    OpenSUSE 13.1 x64 on a Asrock H87 Performance, 8Go RAM, Intel core i5 4670, GTX 670. Dual boot Windows 8.1, two separate hard drives.

  2. #2
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    Default Re: 13.1 : dual boot, btrfs and root partition

    There is no way to boot from a btrfs partition as it cannot support booting. You can use btrfs for the root partition, but you will need a separate /boot partition formatted to another file system e.g. ext4. Mine uses uses ext2 and is 500MB. You need enough to support multiple kernels and 300MB would probably suffice.
    You would install grub onto the /boot partition. However some further planning is also needed.

    If you install btrfs to the root partition, by default Snapper is installed and you should plan to double your normal root partition size to allow for snapshotting whenever YaST or zypper is used to make changes to the system. e.g. 20 GB would be a minimum for that, and you might also need to reconfigure Snapper's default settings for snapshot retention and cleanup, in order to avoid running out of space and breaking your system.

    A separate /home is excluded from snapshotting by default. You can also disable Snapper from any snapshotting even for the system partition, and just use btrfs on root and home partitions.

    The details can be found in official openSUSE documentation at Chapter 4. Snapshots/Rollback with Snapper.

    You may also have seen 3.1.2.1 Btrfs Partitioning in Chapter 3. Advanced Disk Setup.

  3. #3
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    Default Re: 13.1 : dual boot, btrfs and root partition

    Had I have read the f* manual more thoroughly, I'd have been able to solve this on my own ...

    Thanks a lot anyway for taking the time to give me detailed info, much appreciated !
    OpenSUSE 13.1 x64 on a Asrock H87 Performance, 8Go RAM, Intel core i5 4670, GTX 670. Dual boot Windows 8.1, two separate hard drives.

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    Default Re: 13.1 : dual boot, btrfs and root partition

    Quote Originally Posted by AKoine View Post
    Had I have read the f* manual more thoroughly, I'd have been able to solve this on my own ...

    Thanks a lot anyway for taking the time to give me detailed info, much appreciated !
    Indeed, even good "reference" manuals (IMO that one is) need repeat readings for actual implementation . Thanks for your comments.

    In fact, for others reading this thread, I missed out the [additional] hourly snapshots you get when Snapper is active by default on a btrfs root partion. It contributes to the double-size "rule of thumb". I believe the frequency of capture cannot be configured, but the number retained can definitely be changed for the cleanup (a daily cron job).

  5. #5
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    Default Re: 13.1 : dual boot, btrfs and root partition

    Just an FYI
    but with btrfs you do not really need /home partition. you can use a /home sub-volume instead.
    the only features that is not compatible with btrfs are Booting and swap.
    so for booting as itt said above you need to create a /boot partition with other FS
    and swap partition is also need to be created as it's own space.

  6. #6
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    Default Re: 13.1 : dual boot, btrfs and root partition

    Quote Originally Posted by vl1969 View Post
    Just an FYI
    but with btrfs you do not really need /home partition. you can use a /home sub-volume instead.
    That is right. So for those using Snapper on a root partition with /home included, making /home a sub-volume is the way to exclude it from those hourly system snapshots. Why exclude? Typically /home contains large static files for multimedia and perhaps for downloaded .iso images and other stuff. To include it would increase significantly and unnecessarily the size of system snapshots and performance overhead.

  7. #7
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    Default Re: 13.1 : dual boot, btrfs and root partition

    What happens to a sub-volume when you format / it to do a clean install of the next version??


    BTRFS looks like a swiss army knife to me and you know swiss army knives are not the best knives

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    Default Re: 13.1 : dual boot, btrfs and root partition

    Quote Originally Posted by gogalthorp View Post
    What happens to a sub-volume when you format / it to do a clean install of the next version??
    A good question to which I don't know the answer, without researching sub-volumes further. There is a long thread (btrfs as default file system?) in Pre-release forum, including short discussion on the impact of formatting a btrfs partition wrt to recovery using a previous system snapshot. Although it may not have covered sub-volumes specifically.

    One doesn't lose the option to configure /home as a separate partition formatted with btrfs or any other file system type.

    For testing btrfs with Snapper, I used 12.3 (clean-install) with /home on the root partition, openSUSE installer formatted btrfs, and /home set as a sub-volume. After a dist-upgrade to Tumbleweed and regularly applying masses of updates [using zypper dup], I recently chose dist-upgrade again for reaching 13.1, in order to test the impact of a major upgrade on Snapper, disk usage, and partition sizing. So for all that, the clean-install and /home questions just didn't arise.

  9. #9
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    Default Re: 13.1 : dual boot, btrfs and root partition

    Quote Originally Posted by gogalthorp View Post
    What happens to a sub-volume when you format / it to do a clean install of the next version??
    I don't know the answer. But I have an impression that the old filesystem is not erased, and at least some snapshots are retained. So I guess that sub-volumes are also retained.

    Quote Originally Posted by gogalthorp View Post
    BTRFS looks like a swiss army knife to me and you know swiss army knives are not the best knives
    That seems like an apt description.

    I experimented with "btrfs" for 13.1 Beta1 and 13.1 RC1. However, I'm back at "ext4" for 13.1 final. And that probably tells you something about my opinion of "btrfs".
    openSUSE Leap 15.1; KDE Plasma 5;
    testing Leap 15.2Alpha

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    Default Re: 13.1 : dual boot, btrfs and root partition

    Quote Originally Posted by nrickert View Post
    But I have an impression that the old filesystem is not erased, and at least some snapshots are retained.
    I don't see how that impression can hold up.

    Snapshots are stored within the same partition, so the system snapshots will be in the root partition. If you reformat a btrfs partition, all data in the file system would be irreversibly lost. My understanding is that sub-volumes just work at the logical level, you can add and remove them with YaST Partitioner but not format or reformat them in any way. They are just a useful tecnique, e.g. for preventing /var and other system directory structures from inclusion in snapshots, where openSUSE does the obvious ones by default but it's a user choice to do /home or not.

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