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--- linux:fs:btrfs_as_root [2015/07/17 06:25]
127.0.0.1 external edit
+++ linux:fs:btrfs_as_root [2017/01/18 21:41] (current)
niziak
@@ Line 1: / Line 1: @@
-=== System overview ===
+====== BTRFS as root filesystem ======
+===== System overview =====
   - /dev/sda1 4.08GB ext4 "/" used 1.56GB, free 2.53GB
   - /dev/sda2 10.91GB extended
@@ Line 5: / Line 7: @@
     - /dev/sda6 10.40GB ext4 "/home" 321MB used, 10.09GB free
-=== Boot from live-cd ===
+===== Boot from live-cd =====
 Btrfs support is heavily developed in Linux Kernel. So do not use old kernel.
 I was using gparted-live-0.22.0-1-amd64.iso
 (NOTE: to match your existing system architecture (i586, amd64, etc))
 Which contains:
   - Kernel 3.16.0-4-586
   - btrfs utils version 3.17
-=== Conversion ===
-fsck -f /dev/sda1
-fsck -f /dev/sda6
-btrfs-convert /dev/sda1
-Disk usage before conversion: used 1.56GB, free 2.53GB
+===== Update to kernel 4 =====
-after conversion: used 1.65GB, free 2.43GB
-btrfs check /dev/sda1
-=== Update system ===
-Mount new root filesystem:
-mount /dev/sda1 /mnt
-for i in dev dev/pts proc sys ; do mount --bind /$i /mnt/$i ; done
-chroot /mnt
-get new UUID of /dev/sda1 using "blkid"
-mount /dev/sda1 somewhere, go to etc/fstab and update to new UUID:
-UUID=a74f5787-aee1-4981-b7e6-fbd3cb6ac919 /               btrfs    defaults 0       1
-update-grub
-grub-install /dev/sda
-exit
-reboot
-and remove Live CD with Gparted
-Rollback to ext2 is possible. There is subvolume ext2_saved on filesystem
-# btrfs subvolume list /
-To delete backup
-# btrfs subvolume delete /ext2_saved
-=== Redundancy ===
-=== Prepare 2nd disc ===
-Lets assume that we have 2nd disc for other than system stuff, but we want
-to use it as backup solution for system disc. System should be able to boot if one
-disc fails.
-"By default, metadata will be mirrored across two devices and data will be striped across all of the devices present.
-If only one device is present, metadata will be duplicated on that one device. "
-Make second disc bootable:
-grub-install /dev/sdb
-Now we have running and bootable system from BTRFS at /dev/sda1
-Add second device to / volume. Device is unformatted, only partitioned.
-btrfs device add /dev/sdb1 /
-# btrfs filesystem show
-Label: none  uuid: 2a3f41d6-571c-4ed5-91f1-ca5f5c1d3b5e
-    Total devices 2 FS bytes used 1.37GiB
-    devid    1 size 4.08GiB used 4.08GiB path /dev/sda1
-    devid    2 size 5.00GiB used 0.00B path /dev/sdb1
-Btrfs v3.17
-Replicate data to second volume.
-General command:
-btrfs balance start -d <filter> -m <filter> /
-Starts balance action on data (-d) and metadata (-m).
-For details please look into man btrfs balance
-Full command:
-btrfs balance start -dconvert=<profile> -mconvert=<profile> /
-Possible profiles are: raid0, raid1, raid10, raid5, raid6, dup, single
-single - is to put single copy of data (not stripping) and duplicated metadata
-dup - duplicate metadata - but it is not guaranteed that metadata is duplicated on separate devices
-"For now, RAID-1 means 'one copy of what's important exists on two of the drives
-in the array no matter how many drives there may be in it'."
-It is possible to crate raid1 profile in degraded state,
-to add real 2nd hard disc later.
-As 2nd disc use small loop device and after creation remove loop device and remount
-in degraded mode.
-# btrfs fi df /
-Data, single: total=2.69GiB, used=948.35MiB
-System, single: total=32.00MiB, used=4.00KiB
-Metadata, single: total=1.36GiB, used=456.89MiB
-GlobalReserve, single: total=32.00MiB, used=0.00B
-btrfs balance start -dconvert=dup -mconvert=dup /
-=== Error: unable to start balance ===
-ERROR in dmesg:
-[ 2687.757913] BTRFS error (device sda1): unable to start balance with target data profile 32
-Update to kernel 4.0.2 and btrfs-tools v4 doesn't help.
-Probably dup (profile 32) cannot be used for data.
-It works:
-btrfs balance start -dconvert=raid1 -mconvert=raid1 /
-=== Drive fail ===
-Now shutdown system and disconnect 2nd drive
-Boot fail
-BTRFS: failed to read the system array on sda1
-BTRFS: open_cree failed
-And initramfs console appear.
-mkdir /mnt
-mount /dev/sda1 /mnt
-the same error
-mount /dev/sda1 /mnt -odegraded
-WORKS!
-To boot automatically kernel with degraded btrfs, please add "rootflags=degraded" to kernel commandline.
-/etc/default/grub
-GRUB_CMDLINE_LINUX_DEFAULT="quiet rootflags=degraded"
-Add to grub and fstab. Then update grub:
-update-grub
-grub-install /dev/sda
-grub-install /dev/sdb
-Remove missing device :
-btrfs device delete missing /
-Add new disc:
-btrfs device add /dev/sdb /
-Remove missing device - word 'missing' is special device name for this command
-btrfs device delete missing /
-ERROR: error removing the device 'missing' - No space left on device
-There is command
-btrfs replace
-btrfs replace start -r 2 /dev/sdb1 /
-Because device is removed from system followin parameters are used:
--r - use raid redundancy mechanism
-  - dev id
-/dev/sdb1 - new free device (not assigned to any btrfs)
-/ - mount point
-Device needs to be same or greater size, but I made ideal clone of /dev/sda disc using sfdisk and
-above command complains that:
-BTRFS error (device sda1): target device is smaller than source device!
-So I created bigger device and replace process starts. With some errors in dmesg:
-[ 3185.709933] BTRFS: checksum error at logical 6796906496 on dev /dev/sda1, sector 5898312, root 5, inode 163698, offset 244748288, length 4096, links 1 (path: zero)
-[ 3185.711283] BTRFS: bdev /dev/sda1 errs: wr 0, rd 0, flush 0, corrupt 10, gen 0
-[ 3185.712447] BTRFS: unable to fixup (regular) error at logical 6796906496 on dev /dev/sda1
-[ 3190.557027] scrub_handle_errored_block: 4678 callbacks suppressed
-and finally
-[ 3305.403916] BTRFS: dev_replace from <missing disk> (devid 2) to /dev/sdb1 finished
-btrfs replace status /
-Started on 15.Jul 22:38:55, finished on 15.Jul 22:40:55, 0 write errs, 0 uncorr. read errs
-Grub installed to /dev/sda /dev/sdb
-Test - remove sda,
-In grub menu - additional option to boot debian 8 from sdb1 shows.
-Booting from sdb1 stops an initramfs, because option to mount degraded is missing.
-Booting from original options, stuck on
-"A start job is running for dev-disk-by\x2duuid-fb8d9... 55s / 1min 30s"
-After timeout 1:30, system boots into emergency mode.
-"Give root password for maintenance"
-"(or type Control+D to continue)
-journalctl -a
-Jul 16 22:22:17 debian kernel: work still pending
-Jul 16 22:23:43 debian systemd[1]: Job dev-disk-by\x2duuid-fb8d97df\x2d625b\x2d440d\x2db63b\x2dcb529586df24.device/start timed out.
-Jul 16 22:23:43 debian systemd[1]: Timed out waiting for device dev-disk-by\x2duuid-fb8d97df\x2d625b\x2d440d\x2db63b\x2dcb529586df24.device.
-Jul 16 22:23:43 debian systemd[1]: Dependency failed for /home.
-Jul 16 22:23:43 debian systemd[1]: Dependency failed for Local File Systems.
-Jul 16 22:23:43 debian systemd[1]: Dependency failed for File System Check on /dev/disk/by-uuid/fb8d97df-625b-440d-b63b-cb529586df24.
-Jul 16 22:23:43 debian systemd-journal[177]: Runtime journal is using 4.0M (max allowed 9.8M, trying to leave 14.8M free of 94.4M available → current limit 9.
-/lib/systemd/system/local-fs.target
-This is because /home directory is missing (it was located on /dev/sda2)
-but whole /dev/sda removed.
-This bad behaviour, because I want system to be bootable even without additional disc.
-=== TODO ===
-Network in initramfs with SSH to repair remotely
-Network with SSH in maintenance mode
-=== Bulletproof system ===
-Run dropbear on alternative SSH port
-apt-get install dropbear
-/etc/default/dropbear
-=== Update to kernel 4 ===
 Edit /etc/apt/sources and add sid release
+<code bash>
 apt-get update
 apt-get install linux-image-amd64
 apt-get install btrfs-tools
 update-initramfs -u
+</code>
+  * ERROR: Warning: /sbin/fsck.btrfs doesn't exist, can't install to initramfs, ignoring.
+  * EXPLANATION: "This is going to be changed back in the next version of btrfs-tools."
+  * SOLUTION: ln -s /bin/fsck.btrfs /sbin/fsck.btrfs
+Check btrfs-tools version
+<code bash>/bin/btrfs version</code>
-ERROR: Warning: /sbin/fsck.btrfs doesn't exist, can't install to initramfs, ignoring.
-EXPLANATION: "This is going to be changed back in the next version of btrfs-tools."
-SOLUTION: ln -s /bin/fsck.btrfs /sbin/fsck.btrfs
-/bin/btrfs version
+===== Converting dirs into subvolumes  =====
+To make backups, snapshots, moving much easier and faster, every directory you want to backup by snapshot should be a subvolume. Also root filesystem should be created in separate subvolume not in btrfs root.
+To distinguish volumes from directories we will use @ character at beginning of subvolume name. This is Ubuntu naming convention for subvolumes.
+Proposed subvolumes structure (where / is BTRFS root)
+  * /@
+  * /@home
+  * /@var
+Mount BTRFS filesystem (BTRFS root) to /mnt/btrfs.
+==== root ====
+  * take a snapshot of root volume. Name of snapshot is '@'
+    * ''btrfs subvolume snapshot /mnt/btrfs @''
+  * delete files on BTRFS root (/mnt/btrfs)
+  * make @ subvolume a default root
+      * update fstab:<file | /etc/fstab>UUID=739e6086-d925-4bdb-94f5-26d8c10dc171	/ btrfs defaults,subvol=@</file>
+    * OR
+      * get @ subvolume id ''btrfs subvolume list /mnt/btrfs''
+      * set default subvolume to use when system is mounted ''btrfs subvolume set-default 256 /mnt/btrfs''
+==== subdirectories ====
+  * On BTRFS root create a new subvolume
+    * ''btrfs subvolume create /mnt/btrfs/@home''
+  * move files into the new subvolume as if it were a directory
+    * ''mv /mnt/btrs/@/home/* /mnt/btrfs/@home/''
+    * ''cp --reflink'' is much faster on BTRFS
+  * remove old directory
+    * ''rmdir /mnt/btrfs/@/home''
+  * update /etc/fstab to mount @home as /home
+===== fstab ====
+Do not use ''errors=remount-ro'' option which is not valid for BTRFS.
+Example working fstab file:
+<file | /etc/fstab>
+UUID=ed730508-753e-4a7f-ac1e-bf8646f7bd63	/		btrfs		defaults,subvol=@,compress=no				0	0
+UUID=ed730508-753e-4a7f-ac1e-bf8646f7bd63	/var		btrfs		defaults,subvol=@var,compress=no			0	0
+UUID=ed730508-753e-4a7f-ac1e-bf8646f7bd63	/var/log	btrfs		defaults,subvol=@varlog,compress=no			0	0
+UUID=ed730508-753e-4a7f-ac1e-bf8646f7bd63	/home		btrfs		defaults,subvol=@home,compress=no			0	0
+UUID=ed730508-753e-4a7f-ac1e-bf8646f7bd63	/mnt/btrfs	btrfs		noauto,defaults,subvolid=5,compress=no			0	0
+</file>
+To prevent systemd to halt system during startup if device is not found (nofail and x-systemd.device-timeout):
+<file | /etc/fstab>
+UUID=<the_device_uuid> /mount/point btrfs nofail,x-systemd.device-timeout=10,noatime,compress=lzo,autodefrag 0 0
+</file>
+NOTE: do not use autodefrag - it consumes lots of cpu

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