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--- linux:fs:btrfs_as_root2 [2017/01/19 21:56]
niziak [TODO]
+++ linux:fs:btrfs_as_root2 [2021/02/17 08:53] (current)
niziak
@@ Line 52: / Line 52: @@
 **NOTE:** Create subvolumes for things which shouldn't be included in snapshot of parent volume. Like some /var/../cache, etc
+[[https://wiki.archlinux.org/index.php/Snapper#Suggested_filesystem_layout]]
 <code bash>
@@ Line 119: / Line 121: @@
 Create subvolumes:
-<code>
+<code bash>
 cd /mnt
 btrfs subvolume create @pool
@@ Line 130: / Line 132: @@
 </file>
+[[https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Btrfs_on_top_of_dmcrypt]]
 ===== Add 2nd disc =====
-Copy partition layouts from sdb to sda drive:
+See [[btrfs_multidisk]]
-<code bash>
-sudo sfdisk -d /dev/sdb > parts
-sudo sfdisk  /dev/sda < parts
-</code>
-Recreate LVM layout.
-Add 2nd disc to btrfs:
-<code bash>
-btrfs device add /dev/disc1/btrfs1 /
-btrfs device usage /
-btrfs balance start -v -dconvert=raid1 -mconvert=raid1 /
-btrfs device usage /
-</code>
-Let system boot without one disc:
-<file | /etc/default/grub>
-GRUB_CMDLINE_LINUX_DEFAULT="rootflags=degraded"
-</file>
-<code bash>update-grub</code>
-Install grub
-<code bash>
-sudo grub-install /dev/sdb
-sudo grub-install /dev/sdc
-reboot
-</code>
-==== Issues ====
-=== Grub ===
-**PROBLEM**
-**''grub-pc'' 2.02~beta2-22+deb8u1 0** incorrectly handle multiple roots. Internal variable ${GRUB_DEVICE} which is used to generate ''root='' parameter include newline character, so grub menuconfig entry is broken:
-<code>
-       linux<->/@/@root/boot/vmlinuz-4.8.0-0.bpo.2-amd64 root=/dev/mapper/disc2-btrfs2
-/dev/mapper/disc1-btrfs1 ro rootflags=subvol=@/@root  rootflags=degraded
-</code>
-More here: [[https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1238347]] and [[https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1582811]]
-**SOLUTION**
-Fixed in Debian Stretch (testing) version **grub-pc_2.02~beta3-3**
-Now UUID is used multiple roots. UUID of btrfs filesystem placed on 2 disc is the same:
-<code bash>
-/dev/mapper/disc2-btrfs2: UUID="52944cdd-f8d0-4798-bd1c-80539c45253d" UUID_SUB="54703ddb-5789-4cac-bfd0-691acadfa33c" TYPE="btrfs"
-/dev/mapper/disc1-btrfs1: UUID="52944cdd-f8d0-4798-bd1c-80539c45253d" UUID_SUB="9bc49b38-c014-40e3-876e-08f6873293b8" TYPE="btrfs"
-</code>
-So, kernel cmdline parameter **''root=UUID=...''** is now correct.
-=== no symbol table ===
-**PROBLEM**
-Grub says:
-<code>grub error: no symbol table</code>
-**SOLUTION**
-Grub was not reinstalled after update
-<code bash>
-grub-install /dev/sda
-grub-install /dev/sdb
-update-grub
-</code>
-=== ALERT! Dropping to shell! ===
-**PROBLEM**
-Grub loads kernel and initramfs correctly, but:
-''Begin: Waiting for root file system ...'' and Grub still boot into initramfs.
-After some while, initramfs shell is available.
-<code>
-ALERT!
-Dropping to shell!
-</code>
-Unfortunatelly initramfs cannot activate LVM volumes when kernel cmdline ''root=UUID=...'' is used.
-<code bash>
-lvm lvscan
-</code>
-To boot manually:
-<code bash>
-lvm vgchange -ay
-mount /dev/disc2/btrfs2 /root -o device=/dev/disc1/btrfs1
-exit
-</code>
-System should start - but once.
-Problem is located in ''/usr/share/initramfs-tools/scripts/local-top/lvm2''.
-Script check if specified root device needs to be activated by LVM.
-When UUID is used it is executing code:
-<code bash>
-/dev/*/*)
-        # Could be /dev/VG/LV; use lvs to check
-        if lvm lvs -- "$dev" >/dev/null 2>&1; then
-                lvchange_activate "$dev"
-        fi
-        ;;
-</code>
-In result, command
-<code bash>lvm lvs -- disc/by-uuid/52944cdd-f8d0-4798-bd1c-80539c45253d<code>
-is executed, resulting following output:
-<code>"disc/by-uuid/52944cdd-f8d0-4798-bd1c-80539c45253d": Invalid path for Logical Volume.</code>
-Debian bugs about similar problem:
-[[https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=612402]]
-**solution**
-Install lvm2 package version 2.02.168-1 (Debian Stretch). Previously was 2.02.111-2.2+deb8u1 (Debian Jessie).
-<code bash>
-update-initramfs -k all -u
-btrfs scrub /
-</code>
-Also ''GRUB_DISABLE_OS_PROBER=true'' can be added.
-<file | /etc/mkinitcpio.conf>
-BINARIES="/bin/btrfs"
-</file>
-<code bash>update-init -u -k all</code>
-===== Replace bad disc =====
-<code bash>
-btrfs device add /dev/disc3/btrfs3 /
-btrfs device delete missing /
-btrfs fi balance /
-</code>
-<code bash>
-btrfs filesystem show
-btrfs replace start 6 /dev/disc3/btrfs3 /  # change 6 to your setup
-</code>
-==== Fine tuning ====
-  * Add yor ssh public key to ''/etc/initramfs-tools/root/.ssh/authorized_keys''
-  * Change MAC address of eth0 (for initramfs remote access)
-  *
-==== TODO ====
-  * backup GPT header
-  * backup LVM header
-  * backup LUKS header

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