I've booted into the latest nightly build of Fedora and run btrfs rescue 
super-recover -v and also btrfs check.

Super-recover reports that "All supers are valid, no need to recover."  Btrfs 
check displays the same errors as before:

Parent trasid verified failed on xxxx wanted xxxx found xxxxx
Ignoring transid failure
Leaf parent key incorrect xxxxxxx
Bad block xxxxxxxxxxx
Errors found in extend allocation tree or chunk allocation.

The check eventually fails with Segmentation fault (core dumped.)

Attempting to mount with -o recovery results in the error "Can't read 
superblock."  I am able to mount the filesystem read-only however attempting to 
copy all of the data off has been unsuccessful.  It appears to hit a bad area 
and just hangs.

Is there anything else I can try?

Thank you for your insight,

Jeff Michels

-----Original Message-----
From: ch...@colorremedies.com [mailto:ch...@colorremedies.com] On Behalf Of 
Chris Murphy
Sent: Friday, September 16, 2016 7:08 PM
To: Jeffrey Michels
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Filesystem will remount read-only

On Fri, Sep 16, 2016 at 8:57 AM, Jeffrey Michels <jeffr...@skyward.com> 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.

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 

Chris Murphy

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