Btrfs partition gets remounted as read only

Btrfs partition gets remounted as read only

[Incorporeal Waffle]

I tried converting my root partition (originally ext4) to btrfs.

When I booted, I discovered that my root partition is getting
remounted as read only.
I tried to remount it with sudo mount -o remount,rw /
Didn't help. Caused some stuff to appear in dmesg though.
What do?

uname -a; btrfs --version; btrfs fi show; btrfs fi df / ; dmesg
https://mindcraft.si.eu.org/ZeroBin/?7d5c9ba64101c19f#xdhsouft1o7z+j+0dC3c2J5yM8bRuHrPxre/Klf+FWk=
The last part of the dmesg is when I tried to remount it as rw

Re: Btrfs partition gets remounted as read only

[Marc MERLIN]

On Mon, Sep 21, 2015 at 02:30:21PM +0000, Incorporeal Waffle wrote:
> I tried converting my root partition (originally ext4) to btrfs.
> 
> When I booted, I discovered that my root partition is getting
> remounted as read only.

I'm afraid, last I heard, the ext4 convertion stuff was broken, and had been
for a quite a while.
https://btrfs.wiki.kernel.org/index.php/Conversion_from_Ext3

The comment says 4.0, but I've had it fail with older versions of the
kernel.

Try the rollback explained in the wiki
btrfs-convert -r /dev/xxx

If that fails (hopefully not), you'll have to go back to backups.

Sorry,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/  

Re: Btrfs partition gets remounted as read only

[Duncan]

Incorporeal Waffle posted on Mon, 21 Sep 2015 14:30:21 +0000 as excerpted:

> I tried converting my root partition (originally ext4) to btrfs.

There's some known bugs with btrfs-convert currently, with current or 
very recent discussion on-list about how to fix it, if you check the 
archives.

In the more general case, while the present bugs will no doubt be fixed, 
I (a user, not a dev) don't recommend using convert, as in the best case, 
it's a compromise, with better results if you treat the existing ext* as 
a backup and start with a brand new btrfs using mkfs.btrfs.

The admin's rule of backups states that if you care about the data, it's 
backed up, and if it's not backed up, in practice, you're defining the 
data as not worth the time and resources to back up, any claims to the 
contrary not withstanding.  (Meanwhile, a would-be backup that hasn't 
been tested restorable isn't considered a backup, because the backup 
isn't defined as complete until it is tested.)

>From that perspective, there's little reason to do a filesystem 
conversion, since if you care about the data, it's backed up and can be 
restored to a brand new filesystem, with a better layout than a 
filesystem that started as something else is likely to ever achieve, and 
if you don't care about the data, then there's no reason not to start out 
with a clean filesystem in the first place.

So while having a convert tool is "nice", even when it's working 
correctly, the best choice is to avoid using it, starting with brand new 
clean filesystem and copying existing data, if any, into it from backups 
so it is laid out ideally for the new filesystem, instead of the 
compromise of trying to work around the location of existing data and 
metadata, in a layout that should work, granted (and it's definitely a 
bug that it's not doing so today), but is unlikely to be ideal for a 
different filesystem than the one it started out as.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

Re: Btrfs partition gets remounted as read only

[Hugo Mills]

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(Adding OP back to cc list -- I know from IRC they're not subscribed
to the list)

On Mon, Sep 21, 2015 at 03:02:23PM +0000, Duncan wrote:
> Incorporeal Waffle posted on Mon, 21 Sep 2015 14:30:21 +0000 as excerpted:
> 
> > I tried converting my root partition (originally ext4) to btrfs.
> 
> There's some known bugs with btrfs-convert currently, with current or 
> very recent discussion on-list about how to fix it, if you check the 
> archives.
> 
> In the more general case, while the present bugs will no doubt be fixed, 
> I (a user, not a dev) don't recommend using convert, as in the best case, 
> it's a compromise, with better results if you treat the existing ext* as 
> a backup and start with a brand new btrfs using mkfs.btrfs.
> 
> The admin's rule of backups states that if you care about the data, it's 
> backed up, and if it's not backed up, in practice, you're defining the 
> data as not worth the time and resources to back up, any claims to the 
> contrary not withstanding.  (Meanwhile, a would-be backup that hasn't 
> been tested restorable isn't considered a backup, because the backup 
> isn't defined as complete until it is tested.)
> 
> From that perspective, there's little reason to do a filesystem 
> conversion, since if you care about the data, it's backed up and can be 
> restored to a brand new filesystem, with a better layout than a 
> filesystem that started as something else is likely to ever achieve, and 
> if you don't care about the data, then there's no reason not to start out 
> with a clean filesystem in the first place.
> 
> So while having a convert tool is "nice", even when it's working 
> correctly, the best choice is to avoid using it, starting with brand new 
> clean filesystem and copying existing data, if any, into it from backups 
> so it is laid out ideally for the new filesystem, instead of the 
> compromise of trying to work around the location of existing data and 
> metadata, in a layout that should work, granted (and it's definitely a 
> bug that it's not doing so today), but is unlikely to be ideal for a 
> different filesystem than the one it started out as.
> 

-- 
Hugo Mills             | vi vi vi: the Editor of the Beast.
hugo@... carfax.org.uk |
http://carfax.org.uk/  |
PGP: E2AB1DE4          |

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