====== BTRFS ======

===== References =====
[[https://www.howtoforge.com/a-beginners-guide-to-btrfs]] \\
[[https://www.howtoforge.com/how-to-convert-an-ext3-ext4-root-file-system-to-btrfs-on-ubuntu-12.10]] \\
[[http://www.oracle.com/technetwork/articles/servers-storage-admin/advanced-btrfs-1734952.html]] \\

[[https://btrfs.wiki.kernel.org/index.php/Compression|Compression]]



Create BTRFS filesystem on multiple block devices:
<code>
 mkfs.btrfs  /dev/loop0 /dev/loop1
</code>

<code>
btrfs filesystem show /dev/loop0
Label: none  uuid: e9a456cd-57d7-4355-a20a-77243d66722e
        Total devices 2 FS bytes used 28.00KiB
        devid    1 size 200.00MiB used 12.00MiB path /dev/loop0
        devid    2 size 200.00MiB used 0.00B path /dev/loop1
</code>

As you can see, every block belongs to FS can be used. Also for mount:

<code>mount /dev/loop0 /BTRFS</code>
or
<code>mount /dev/loop1 /BTRFS</code>

===== Swap support =====

**Current state:** Do not create SWAP files on BTRFS!

Swap support was restored with Kernel 4.21


===== Add/remove block devices =====
Add new block device (extend size)
<code> btrfs device add /dev/loop2 /BTRFS</code>

Remove device:
<code>btrfs device delete /dev/loop0 /BTRFS</code>

!!! It is possible to remove any device if there is free space to which data can be moved during removal.


====== Scrub ======

Start foreground, readonly scrub, print statistics at end:
<code bash>
btrfs scrub start -B -d -r /

scrub device /dev/sda3 (id 1) done
	scrub started at Mon Mar  6 07:02:56 2017 and finished after 00:04:06
	total bytes scrubbed: 18.50GiB with 0 errors
scrub device /dev/sdc5 (id 2) done
	scrub started at Mon Mar  6 07:02:56 2017 and finished after 00:06:52
	total bytes scrubbed: 18.47GiB with 0 errors

</code>

Get currently running scrub status:
<code bash>btrfs scrub status /</code>


====== migration to BTRFS ======

<code bash>apt-get install btrfs-tools</code>

====== Issues ======

===== Compression type 0x3 not supported =====

GRUB 2.02 doesn't support ZSTD compression.
Solution is to exlude ''/boot'' from ZSTD compression (below) or install more recent Grub (from Debian Bullseye)
<code bash>
sudo btrfs filesystem defragment -v -r -czlib /boot
sudo btrfs property set /boot compression zlib
# disable compression for newly created files
chattr -Rc /boot
</code>

===== error inheriting props for ino 3336468 (root 264): -28 =====
<code c>
 31 #define ENOSPC          28      /* No space left on device */
</code>
<code bash>
# btrfs fi show /mount
Label: none  uuid: 5db83d5e-4f38-40b0-ac5d-dadd9cd1d23f
	Total devices 1 FS bytes used 22.18GiB
	devid    1 size 30.00GiB used 27.58GiB path /dev/mapper/vg_spox-lv_home

# btrfs fi usage /mount
Overall:
    Device size:		  30.00GiB
    Device allocated:		  27.58GiB
    Device unallocated:		   2.42GiB
    Device missing:		     0.00B
    Used:			  22.52GiB
    Free (estimated):		   5.58GiB	(min: 4.37GiB)
    Data ratio:			      1.00
    Metadata ratio:		      1.99
    Global reserve:		 512.00MiB	(used: 0.00B)

Data,single: Size:25.01GiB, Used:21.84GiB
   /dev/mapper/...	  25.01GiB

Metadata,single: Size:8.00MiB, Used:0.00B
   /dev/mapper/...	   8.00MiB

Metadata,DUP: Size:1.25GiB, Used:348.23MiB
   /dev/mapper/...	   2.50GiB

System,single: Size:4.00MiB, Used:0.00B
   /dev/mapper/...	   4.00MiB

System,DUP: Size:32.00MiB, Used:16.00KiB
   /dev/mapper/...	  64.00MiB

Unallocated:
   /dev/mapper/...	   2.42GiB

</code>

[[https://bbs.archlinux.org/viewtopic.php?id=200817]]
[[http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg60637.html]]