From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f194.google.com ([209.85.213.194]:36117 "EHLO mail-ig0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752186AbcDRPRX (ORCPT ); Mon, 18 Apr 2016 11:17:23 -0400 Received: by mail-ig0-f194.google.com with SMTP id kb1so11285926igb.3 for ; Mon, 18 Apr 2016 08:17:23 -0700 (PDT) Subject: Re: Install to or Recover RAID Array Subvolume Root? To: Chris Murphy References: <5714D39B.90402@gmail.com> Cc: David Alcorn , Btrfs BTRFS From: "Austin S. Hemmelgarn" Message-ID: <5714FA2F.6010207@gmail.com> Date: Mon, 18 Apr 2016 11:15:59 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2016-04-18 11:12, Chris Murphy wrote: > On Mon, Apr 18, 2016 at 6:31 AM, Austin S. Hemmelgarn > 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.