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#format wiki
#language en
= 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 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
}}}



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