On 2016-04-18 11:12, Chris Murphy wrote:
On Mon, Apr 18, 2016 at 6:31 AM, Austin S. Hemmelgarn
<ahferro...@gmail.com> wrote:
On 2016-04-18 01:22, David Alcorn wrote:
I erred and shutdown my NAS during a balance. Grub lost track of my
root. Root was on RAID 6 array subvolid 257. I can boot a different
root from a USB flash drive but neither update-grub not install-grub
sees my old root on array subvolid 257. I am happy to either recover
or lose array subvolid 257 but do not want to lose data on other array
subvol's. I prefer to have my root on the array rather than a flash
drive. The balance completed successfully after I booted from the
flash drive.
I am running a debian back-ported 4.4.0 kernel with btrfs-progs v4.4
on both my flash drive and array subvolid 257. Both installs are
UEFI.
It's rather refreshing to see somebody using an up to date kernel and
userspace for once. The issue with GRUB is however likely an issue with
GRUB itself though (or possibly with something it uses for detecting
filesystems), which brings up the question: How recent is the version of
GRUB you're trying to install? I would not be surprised if their current
support for BTRFS raid5 and raid6 is not particularly good, especially
considering that their support for BTRFS raid1 was kind of shoddy at first
(and it still has occasional issues, like not working right half the time if
one of the devices is missing).
I can't tell if this setup is Btrfs on md/mdadm raid6, or if it's
Btrfs raid6? GRUB has supported mdadm raid6 for a long time, but I
don't think it understands Btrfs raid56 at all.
The only GUI installer I know that explicitly permits installation of
an OS to an existing Btrfs is Anaconda (mainly Red Hat and Fedora).
There's a bug in the storage backend that prevents this from working
in Fedora 23, exposed by a Btrfs change disallowing simultaneous use
of subvolid and subvol, resulting in mount failure, which in turn
causes the installer to crash. But it works in Fedora 22, and it will
work in Fedora 24. On the other hand, no Fedora supports Btrfs for
/boot, it has to be separate and it has to be ext4 or XFS (and maybe
FAT).
I don't know about the current state of the Debian installer, but I know
back when I used Debian regularly and used the standard text based
installer, as long as I didn't format things from the UI, I could
provision the filesystems however the hell I wanted manually and point
the installer at the appropriate ones for each mount point, and it worked.
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