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As a test I want to install Ubuntu 11.10 onto a btrfs file system in raid10 mode. However, I have no clue on how I should go about that. I have tried the installer, and then creating the fs in the terminal. However, that didn't work out. When I went back to the graphical interface I couldn't install. Because it didn't have any mount points. So, how should I do this?

After using the alternate installer and dropping to a shell I did the following: mkfs.btrfs -m raid10 -d raid10 /dev/sda /dev/sdb /dev/sdc /dev/sdd then you also need to run: btrfs dev scan

Then when choosing the partition to install to, select one of the above and mount that to /. Leave all partitions untouched.

This installs the system, however, installing the bootloader fails...

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What didn't work when you created the filesystem from the terminal? Can you update your question with that info? –  JanC Dec 12 '11 at 19:41
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2 Answers

up vote 7 down vote accepted

OK, part of my problem was that I wanted to install Ubuntu Server. I have finally succeeded. To install Ubuntu Server on btrfs RAID10, use the following steps:

  1. Run the livecd of Ubuntu Desktop
  2. Use gparted to create btrfs partitions on all the disks you want to use in the btrfs RAID10 setup, be sure to leave 1 MB at the beginning of the disks for GRUB. (I leave 1 MB on all the disks, so that I could always move grub to another disk, when I replace a disk with a new/larger one.
  3. Save the new partition table
  4. shutdown
  5. launch the Ubuntu server installer
  6. at the partitioning step, break out of the installer and go to the terminal
  7. in the terminal type the following command to create a btrfs RAID10 for data and metadata (Note use the partitions, not the disks!):

    mkfs.btrfs -m raid10 -d raid10 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
    
  8. IMPORTANT execute the following command: btrfs dev scan

  9. go back to the partition part of the installer
  10. select any one disk and choose to use that as btrfs and mountpoint root
  11. proceed installer as normal

So this works fine, however, I later found out that this does not do what I had expected. I have 16-G, 500G and 2x 750G hard disks.

I expected to be able to use 910G. However, raid is a bit different in btrfs I got 320G. What I wanted to use is raid1, because this will create 2 copies of each data block, even if you add 4 disks (unlike the normal raid1). So now, using raid1 in btrfs I do get the 910G.

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I have spent a couple of hours in trying to install Ubuntu 12.04 Beta 2 Server on a RAID-1 btrfs system. The answer of balchmar has helped me a lot, thanks! However, I ended up using a slightly different approach and wanna mention it here for completeness:

  1. Prepare your disk partitioning.
    You can use the LiveCD or -as in my case- a previously installed 12.04 Ubuntu server installation. Important: I had to learn that, contrary to what is mentioned in the btrfs wiki, I had to use partitions instead of entire devices like /dev/sda, so that grub can install into the MBR by the Ubuntu Installer. So, here's the partition I used. Note that I use two identical 500GB disks and two partitions each, one for btrfs and one for swap:

    Disk /dev/sda: 500.1 GB, 500107862016 bytes
    255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
    
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0x0004f49a
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/sda1   *        2048   945508351   472753152   83  Linux
    /dev/sda2       945508352   976771071    15631360   82  Linux swap / Solaris
    
    Disk /dev/sdb: 500.1 GB, 500107862016 bytes
    255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0x0002505f
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/sdb1            2048   945508351   472753152   83  Linux
    /dev/sdb2       945508352   976771071    15631360   82  Linux swap / Solaris
    
  2. Start a default Ubuntu 12.04 Server installation until the disk partition part. Don't make any selection there yet.

  3. Press CTRL-ALT-F2 and enter the console. Issue the following commands, which will create a RAID-1 btrfs filesystem over /dev/sda1 and /dev/sdb1, labeling it RAID1:

    make.btrfs -L RAID1 -m raid1 -d raid1 /dev/sda1 /dev/sdb1 && btrfs device scan

  4. Press CTRL-ALT-F1 to go back to the installer and choose to manually partition your disk.

  5. You can now choose /dev/sda1 and define the mount point '/'. Important: Do not choose to format the file system as this would delete your previously created RAID-1 one! (you may now also choose to make use of the previously defined swap devices, of course.)

  6. Continue the installation as normal. All data will be now installed on your RAID-1 btrfs!

  7. Not sure this is needed, but some people mention one has to run

    btrfs filesystem balance

after the initial boot. You can check the result by issuing the following command:

$ sudo btrfs filesystem show

Label: 'RAID1'  uuid: 49d2eaed-d598-462f-a768-e6e0d43dc7ce
       Total devices 2 FS bytes used 635.45MB
       devid    1 size 450.85GB used 1.26GB path /dev/sda1
       devid    2 size 450.85GB used 1.26GB path /dev/sdb1

Btrfs Btrfs v0.19

To see that RAID-1 is actually used for data and metadata, issue

$ sudo btrfs filesystem df /

Data, RAID1: total=1.00GB, used=568.07MB
System, RAID1: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=256.00MB, used=67.37MB
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