BTRFS filesystem

Links: Linux/Btrfs/UbuntuExt4ToBtrfs, docker/docker-btrfs , linux/btrfs/crash201706 , https://wiki.debian.org/Btrfs
Btrfs space calculator http://carfax.org.uk/btrfs-usage/
- MODE: single=use all, raid0=smallest disk striped, raid1=2copy(smallest of biggest disk and rest)

Create a raid1 mirror disk setup raid1 for both data and metadata

mkfs.btrfs -m raid1 -d raid1 /dev/sdb /dev/sdc /dev/sdd /dev/sde

Now find uuid with sudo blkid /dev/sd*

Add more hd's

       btrfs device scan
       btrfs filesystem show /
       btrfs device add /dev/sdc2 /
       btrfs filesystem balance /
       btrfs balance start -dconvert=raid1 -mconvert=raid1 /
       #Monitor progress with
       btrfs balance status /

reflinks
- cp --reflink name1 name4
- reflinks are supported by BTRFS and OCFS2 and support transparent copy on write which is especially useful for snapshotting.
- Note that since separate inodes are used, one can have different permissions to access the same data.
- Reflinks have the same use as hardlinks, but are more space efficient and generally handle all subsequent operations on a file, not just unlink().
If you have virtual images on a btrfs, cow(copy on write) will cause a lot of fragmentation, turn it of for the directory of file with
- this disables cow(fragmentation) and also crc calculations on the files.
  - ```
       chatter +C /path
```

defrag with

   btrfs filesystem defragment /path/file

or faster for large files

     cp --reflink=never vbox.vdi vbox.new.vdi ; rm vbox.vdi ;

Create raid array, raid1 all data mirrored once.
- # mkfs.btrfs -m raid1 -d raid1 -L root /dev/disk/by-label/root1 /dev/disk/by-label/root2 /dev/disk/by-lab

el/root3 /dev/disk/by-label/root4

Mount options, add compress
subvolumes
- mount option subvol=homevol

Install on multi disk

Will install on multiple disks
- ```
   sudo dpkg-reconfigure grub-pc 
```
Use uuid , same for all disks.
- ```
   sudo blkid /dev/sd* 
```

BTRFS maintenace

SCRUB disks in background, recovering for good copy in raid1 config

   sudo btrfs filesystem show
   sudo btrfs filesystem df /
   sudo btrfs scrub start /
   sudo btrfs scrub status -d /
   sudo btrfs device stats /

Resize
1. Increase the partition (lvm or fdisk)
2. find the <devid> (disk number) # btrfs filesystem show
3. btrfs filesystem resize <devid>:max /

Error trying to convert to raid0

   # btrfs balance start -dconvert=raid0 /home
   ERROR: error during balancing '/home' - No space left on device
   In dmesg  btrfs: 262 enospc errors during balance

FIX

  sudo btrfs fi balance start -dusage=10 /
  btrfs balance start -dconvert=raid0 /home

Remove a drive for a array. Can take long, as data is moved off.
- ```
btrfs fi show
btrfs device delete /dev/sde1 /
```
if single disk in raid1 fails, best course of action if you can replace the broken disk immediately is to convert to single drive.
```
btrfs balance start -dconvert=single -mconvert=dup /whatever
```

Problem with filesystem full

2016-03 a big struggle with a full btrfs root fs and then corrupt grub2 on top of the problem.
- grub rescue>
  - used >set prefix=hd(0,1)/@snapxxxxx/boot/grub
  - This loaded old non corrupt grub2 normal module and typing normal, loaded old bootloader yeah for btrfs.
  - then at the grub2 menu, edit the boot parameters to put root at /@ and load newer kernel from corrupt root fs.
- Space Solved with removing snapshots and deleting some files, then re-balance.
  - To delete snapshot's you need to mount disk to get to subvolumes.
    - No space to create dir, mount over root with mount /dev/sda1 /root
    - Delete subvolumes with #btrfs subvolume delete /root/@snapshot*

HP Server Raid tools

http://dmatwork.blogspot.com/2010/07/installation-of-hp-array-configuration.html

Check disk with smartctl

Check with systemctl

sudo btrfs filesystem show

sudo apt install smartmontools
sudo systemctl start smartd
sudo smartctl -H /dev/sda2

#Test
sudo smartctl -t short -a /dev/sdX

...