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#1 2015-04-11 17:44:15

analbeard
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From: London
Registered: 2014-11-07
Posts: 48

Migrating / from ext4 to btrfs - where did I go wrong?

OK, so I made the various btrfs subvols and mounted them up, rsynced the file system back over, re-created the fstab with UUIDs, then chrooted in to update grub and rebuild the initramfs.

On boot, I get GRUB telling me 'no such device' and then a UUID.

What have I missed?


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#2 2015-04-11 17:53:46

WorMzy
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Re: Migrating / from ext4 to btrfs - where did I go wrong?

Does the UUID match that of a filesystem? Is it the root filesystem? When you're dropped to the initramfs prompt or emergency shell, can you see this UUID listed under /dev/disk/by-uuid?


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#3 2015-04-11 21:16:30

analbeard
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From: London
Registered: 2014-11-07
Posts: 48

Re: Migrating / from ext4 to btrfs - where did I go wrong?

OK, so I sussed that the UUID it didn't recognise was that of my USB Arch live disk - not sure how I managed that, must've generated grub.cfg from outside the chroot by mistake.

I'm more or less sorted, apart from one small issue. I have a couple of subvolumes for /etc and /var/ and these don't appear to be being mounted on boot - i am prompted to enter some information for my 'first boot' into my 'new' system. If I jump back into the live USB I can see a very sparse set of files in /etc before the subvol is mounted - far less than my subvol contains. I cannot see anything in the boot process referencing mounting the subvolumes either.

The two subvols are in the fstab, but they have the same UUID as / (with the subvol named in the options) - is this correct?

Last edited by analbeard (2015-04-11 21:17:21)


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#4 2015-04-11 21:22:20

Scimmia
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Registered: 2012-09-01
Posts: 11,461

Re: Migrating / from ext4 to btrfs - where did I go wrong?

Why wouldn't you just make them subvolumes inside the root subvolume? Or really, why make the separate subvolumes at all?

Last edited by Scimmia (2015-04-11 21:23:41)

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#5 2015-04-12 09:08:29

analbeard
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From: London
Registered: 2014-11-07
Posts: 48

Re: Migrating / from ext4 to btrfs - where did I go wrong?

Scimmia wrote:

Why wouldn't you just make them subvolumes inside the root subvolume? Or really, why make the separate subvolumes at all?

I was following this: https://wiki.archlinux.org/index.php/Bt … _subvolume

I want separate subvolumes to make a rollback easier if something goes wrong during an upgrade, and because I'm limited on disk space so I want pacman's cache to be constrained.

Are you saying the information on the wiki isn't correct?


Edit: I've been doing some more reading, and it appears some people make etc and var (in my case) as subvolumes under / - I wasn't aware this was possible. Is this what you were referring to in the first line of your reply above?

Last edited by analbeard (2015-04-12 09:57:22)


Late 2016 Dell XPS15 | i7-6700HQ | 16GB DDR4 | Samsung PM961 NVMe 512Gb SSD
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#6 2015-04-12 15:38:38

Scimmia
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Registered: 2012-09-01
Posts: 11,461

Re: Migrating / from ext4 to btrfs - where did I go wrong?

Yes, some of that information isn't totally accurate. It's how one person thought things should be set up, nothing more. And yes, I was talking about making subvols under /. This isn't LVM, BTRFS has more flexibility in this regard.

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