Re: system hangs due to qgroups

[Marc Joliet <marcec@gmx.de>]

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On Sunday 04 December 2016 18:24:08 Duncan wrote:
> Marc Joliet posted on Sun, 04 Dec 2016 17:02:48 +0100 as excerpted:
> > That's a good idea, although I'll probably start with sysrescuecd (Linux
> > 4.8.5 and btrfs-progs 4.7.3), as I already have experience with it.
> > 
> > [After trying it]
> > 
> > Well, crap, I was able to get images of the file system (one sanitized),
> > but mounting always fails with "device or resource busy" (with no
> > corresponding dmesg output).  (Also, that drive's partitions weren't
> > discovered on bootup, I had to run partprobe first.)  I never see that
> > in the initramfs, so I'm not sure what's causing that.
> 
> If I understand correctly what you're doing, that part is easily enough
> explained.
> 
> Remember that btrfs, unlike most filesystems, is multi-device capable.
> The way it tracks which devices belong to which filesystems is by UUID,
> universally *UNIQUE* ID.  If you image a device via dd or similar, you of
> course image its UUID as well, destroying the "unique" assumption in UUID
> and confusing btrfs, which will consider it part of the existing
> filesystem if the original devices with that filesystem UUID remain
> hooked up.
> 
> So if you did what I believe you did, try to mount the image while the
> original filesystem devices remain attached and mounted, btrfs is simply
> saying that filesystem (which btrfs identifies by UUID) is already
> mounted: "device or resource busy".
[...]

Nope, sorry if I wasn't clear, I didn't mean that I tried to mount the image 
(can you even mount images created with btrfs-image?).  Plus the images are 
xz-compressed.

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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