BTRFS

[faddat]

Hi,

1. Been having some issues with Docker lately
2. Would like to use BTRFS in my images because of bump 1.4 #1 and because BTRFS=better.

There are many ways I could do this, unfortunately most have failed. Do you have a recommendation on a best way to do this?

[moul]

Hi @faddat,

You can try this:

1. service stop docker
2. update the docker configuration in /etc/default/docker
3. rm -rf /var/lib/docker
4. service start docker

(based on https://docs.docker.com/engine/userguide/storagedriver/selectadriver/)

[moul]

1. stop your server
2. attach a secondary nbd device
3. boot
4. mkfs.btrfs /dev/nbd1
5. service stop docker
6. update the docker configuration in /etc/default/docker
7. rm -rf /var/lib/docker
8. `mount /dev/nbd1 /var/lib/docker
9. service start docker

[faddat]

Manfred,

Sorry, but this misses the point of what we wish to do, which is
specifically format the / as btrfs, and use that without a second disk.

Thoughts? Everything I've tried has blown up on me.

Jacob Gadikian
E-mail: faddat@gmail.com
SKYPE: faddat
Phone/SMS: +84 167 789 6421

On Thu, Jun 23, 2016 at 3:44 PM, Manfred Touron notifications@github.com
wrote:

1. stop your server
2. attach a secondary nbd device
3. boot
4. mkfs.btrfs /dev/nbd1
5. service stop docker
6. update the docker configuration in /etc/default/docker
7. rm -rf /var/lib/docker
8. `mount /dev/nbd1 /var/lib/docker
9. service start docker

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[faddat]

so, this is kinda many months later

but-- I'd still like to know how to go about doing this. I'm going to try a deboostrap on the secondary disk after formatting it btrfs and then saving it as an image. Think that will work?

[moul]

It should work. However, your bare debootstrap will probably miss some important scripts, see https://github.com/scaleway/image-ubuntu/blob/master/16.04/Dockerfile#L2 for examples of how we customize the debootstrap

---

In my opinion, it should be a lot easier to use the helpers we added in the initrd; we already have a "live" mode that works like a "live cd", and it supports BTRFS (see https://github.com/scaleway/initrd/blob/master/Linux/tree-common/boot-live).

@QuentinPerez can you provide to @faddat a scw command that runs a server, formats the rootfs in BTRFS and live-installs a rootfs tarball?

[faddat]

Wow that'd be qute a command, if it existed.... I'm trying your "livecd" now. That is a pretty cool concept.

[faddat]

Also.... I keep seeing references made to MIPS..... should this be taken as a hint?

[QuentinPerez]

Hi @faddat,

The following commands, start a fresh xenial server on VC1S, drop a shell in the initrd, backup your rootfs, format /dev/vda in BTRFS and restore your rootfs.

$ scw run -d --name test-btrfs -e "INITRD_DROPBEAR=1" xenial
$ scw exec -w test-btrfs "mkdir -p /tmp/cpy; cp -pr /newroot /tmp/cpy; chroot /tmp/cpy/newroot/ /usr/local/sbin/scw-sync-kernel-modules ; cp -r /tmp/cpy/newroot/lib/modules/ /lib; depmod -a ; mknod /dev/btrfs-control c 10 234 ; umount /dev/vda; mkfs.btrfs -f /dev/vda; mount /dev/vda /newroot/; cp -rp /tmp/cpy/newroot/* /newroot/; continue-boot"
$ scw exec -w test-btrfs "mount | grep btrfs"
/dev/vda on / type btrfs (rw,relatime,space_cache,subvolid=5,subvol=/)

[stuart12]

@QuentinPerez this appears to work. I can create and login to the new server test-btrfs with / on btrfs but when I reboot, the server cannot mount /. It appears that the kernel/initrd after the reboot does not have btrfs available. Have you tried a reboot after having run the above commands? Thanks!

[firegurafiku]

@moul
@QuentinPerez

Let me bump the question up. I've just tried to live-convert root partition from Ext4 to Btrfs with the pivot_root approach (following instructions from this great answer on StackExchange). I managed to convert the filesystem, but got the following error message in boot log:

>>> Initializing 'local' root file system...
>>> Attaching nbd0...
>>> Mounting nbd0 root...
>>> Mounting /newroot...
>>> 'mount /dev/nbd0 /newroot' failed

Are there any options to work around the issue?

Update:

I changed bootscript to armv7l 4.10.8 docker #1 in the machine's advanced settings, and everything started up like a charm!

@faddat

If your problem is still open, this setting may solve it too.

[berezins]

But no luck with VC1S with different bootscripts tried (mainline 4.4, 4.14, docker 4.10 at least). Tried to mount btrfs-formated disk also from initrd shell but it just refuses to mount with strange "No such device" or "Invalid parameter" error, even disk formated with mkfs.btrfs directly from that same initrd shell. While ext4 disks are mounted successfuly from same shell when same disk mkfs.ext4 formatted from there. It looks like there apparently not included something related to btrfs in x86_64 initrd. Did not try armv71 yet just to compare though it's not a solution for me since I need run x86_64 images on Scaleway with BTRFS.