Yep - had just figured that out and successfully booted with it, and was
in the process of typing up instructions for the list (and posterity).
One thing that concerns me is that edits made directly to grub.cfg will
get wiped out with every kernel upgrade when update-grub is run - any
idea where I'd put this in /etc/grub.d to have a persistent change?
I have to tell you, I'm not real thrilled with this behavior either way
- it means I can't have the option to automatically mount degraded
filesystems without the filesystems in question ALWAYS showing as being
mounted degraded, whether the disks are all present and working fine or
not. That's kind of blecchy. =\
On 01/03/2014 06:18 PM, Hugo Mills wrote:
On Fri, Jan 03, 2014 at 06:13:25PM -0500, Jim Salter wrote:
Sorry - where do I put this in GRUB? /boot/grub/grub.cfg is still
kinda black magic to me, and I don't think I'm supposed to be
editing it directly at all anymore anyway, if I remember
correctly...
You don't need to edit grub.cfg -- when you boot, grub has an edit
option, so you can do it at boot time without having to use a rescue
disk.
Regardless, the thing you need to edit is the line starting
"linux", and will look something like this:
linux /vmlinuz-3.11.0-rc2-dirty root=UUID=1b6ec419-211a-445e-b762-ae7da27b6e8a
ro single rootflags=subvol=fs-root
If there's a rootflags= option already (as above), add ",degraded"
to the end. If there isn't, add "rootflags=degraded".
Hugo.
HOWEVER - this won't allow a root filesystem to mount. How do you deal
with this if you'd set up a btrfs-raid1 or btrfs-raid10 as your root
filesystem? Few things are scarier than seeing the "cannot find init"
message in GRUB and being faced with a BusyBox prompt... which is
actually how I initially got my scare; I was trying to do a walkthrough
for setting up a raid1 / for an article in a major online magazine and
it wouldn't boot at all after removing a device; I backed off and tested
with a non root filesystem before hitting the list.
Add -o degraded to the boot-options in GRUB.
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