Re: Filesystem will remount read-only

[Chris Murphy]

On Fri, Sep 16, 2016 at 6:08 PM, Chris Murphy  wrote:
>
> If -o recovery doesn't work, you'll need to use something newer, you
> could use one of:
>
> Fedora Rawhide nightly with 4.8rc6 kernel and btrfs-progs 4.7.2. This
> is a small netinstall image. dd to a USB stick, choose Troubleshooting
> option, then the Rescue option, then after startup use the 3 option to
> get to a shell where you can try to mount normally, or use
> btrfs-check. Limited tty, no sshd.
> https://kojipkgs.fedoraproject.org/compose/rawhide/Fedora-Rawhide-20160914.n.0/compose/Everything/x86_64/iso/Fedora-Everything-netinst-x86_64-Rawhide-20160914.n.0.iso.n.0.iso
>
> Or something more official with published hash's for the image and a
> GUI, Fedora 24 workstation has kernel 4.5.5 and btrfs-progs 4.5.2
> https://getfedora.org/en/workstation/download/

Just to complete the thought... use these just to boot and have access
to something newer. I'm not suggesting install them. First try a
normal mount, and if that fails, try -o recovery, if that fails, I'm
curious about

btrfs rescue super-recover -v 
btrfs check 

What I'm after is a way to get it to mount cleanly with a new kernel,
and then hoping you can then just reboot with the ancient kernel and
it'll be back to normal.


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Re: Filesystem will remount read-only

[Chris Murphy]

On Fri, Sep 16, 2016 at 8:57 AM, Jeffrey Michels  wrote:
> Hello,
>
> I have a system that has been in production for a few years.  The SAN the VM 
> was running on had a hardware failure about a month ago and now one of the 
> two btrfs filesystems will remount after boot read-only.  Here is the system 
> information:
>
> uname -a
>
> Linux retain 3.0.101-0.47.71-default #1 SMP Thu Nov 12 12:22:22 UTC 2015 
> (b5b212e) x86_64 x86_64 x86_64 GNU/Linux
>
> Btrfs --version
>
> Btrfs v0.20+

Impressive that it's been running in production this long and with old
kernel. I like it!

Anyway, you could try mounting with -o recovery and see if that works.
That's about the only thing I'd trust with such an old kernel and
btrfs-progs. I don't even think it's worth trying the btrfsck on v0.20
just to see what the problems might be, and certainly not for actually
using the repair mode.  Actually I'm not even sure progs that old even
does repairs, it might be the era of notify only.

If -o recovery doesn't work, you'll need to use something newer, you
could use one of:

Fedora Rawhide nightly with 4.8rc6 kernel and btrfs-progs 4.7.2. This
is a small netinstall image. dd to a USB stick, choose Troubleshooting
option, then the Rescue option, then after startup use the 3 option to
get to a shell where you can try to mount normally, or use
btrfs-check. Limited tty, no sshd.
https://kojipkgs.fedoraproject.org/compose/rawhide/Fedora-Rawhide-20160914.n.0/compose/Everything/x86_64/iso/Fedora-Everything-netinst-x86_64-Rawhide-20160914.n.0.iso.n.0.iso

Or something more official with published hash's for the image and a
GUI, Fedora 24 workstation has kernel 4.5.5 and btrfs-progs 4.5.2
https://getfedora.org/en/workstation/download/




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Re: Filesystem will remount read-only

[Duncan]

Jeffrey Michels posted on Fri, 16 Sep 2016 14:57:43 + as excerpted:

> Hello,
> 
> I have a system that has been in production for a few years.  The SAN
> the VM was running on had a hardware failure about a month ago and now
> one of the two btrfs filesystems will remount after boot read-only. 
> Here is the system information:
> 
> uname -a
> 
> Linux retain 3.0.101-0.47.71-default #1 SMP Thu Nov 12 12:22:22 UTC 2015
> (b5b212e) x86_64 x86_64 x86_64 GNU/Linux
> 
> Btrfs --version
> 
> Btrfs v0.20+

That is positively /ancient/, both kernel and userspace (btrfs-progs).  
Keep in mind that btrfs was still considered very experimental back then, 
with the experimental labels coming off only with 3.14 or there abouts, 
IIRC (userspace releases got version-synced with kernelspace in 3.12, so 
3.14 applies to both).

So you have been running an at-the-time still extremely experimental 
filesystem for years now, and it's only now coming up with problems that 
need fixed.  Pretty remarkable for the experimental state back then, but 
it doesn't change the fact that it /was/ "may eat your data and burn your 
kids alive as a sacrifice to appease the filesystem gods" level 
experimental, with the according warnings, back then.

So first thing I'd suggest is to update to kernel 4.4 LTS series, and 
something similar for btrfs-progs userspace.  Then, given the age and 
experimental nature of the filesystem back then, I'd kill the filesystems 
and do a fresh mkfs.btrfs, restoring from backups.  That way you're 
starting with a well tested and stable LTS kernel that is both reasonably 
mature already, and will be supported for some time to come, and 
eliminate any possibility of long fixed and forgotten bugs coming back to 
bite you years later.

Alternatively, if you're using a long-term support distro, you have the 
choice of going to them for that support, since unlike this list which 
focuses on the state going forward, that sort of deep long-term support 
of long outdated versions is a good part of the reason such distros 
exist, and a good part of why a lot of people are willing to pay 
sometimes rather sizable sums of money /for/ that level of support.

-- 
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

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