Creating a btrfs volume

# create btrfs FS on sda partition 3

mkfs.btrfs /dev/sda3

Mounting btrfs and Creating a sub-volume

mkdir /mnt/myfs
mount /dev/sda3 /mnt/myfs
cd /mnt/myfs

# Since we're cd'd into /mnt/myfs - this creates a subvolume called `mydata` inside of `/mnt/myfs`

[root@sysresccd /mnt/myfs]# btrfs subvolume create mydata
Create subvolume './mydata'

[root@sysresccd /mnt/myfs]# ls -la /mnt/myfs

drwxr-xr-x  1 root root   14 Aug 15 11:15 .
drwxr-xr-x 14 root root 4096 Aug 15 11:15 ..
drwxr-xr-x  1 root root    0 Aug 15 11:15 mydata

[root@sysresccd /mnt/myfs]# btrfs subvolume list /mnt/myfs
ID 257 gen 8 top level 5 path mydata

Setting a label for a btrfs filesystem

btrfs filesystem label /mnt/myfs "mydata"

# Or, directly on the partition

btrfs filesystem label /dev/sda3 "mydata"

Enable compression for a subvolume / folder using `chattr` (+c - lowercase C = enable compression for NEW files in this folder - will not affect existing files)

[root@sysresccd /mnt/root/var/newlogs]# lsattr
------------------- ./logdata
[root@sysresccd /mnt/root/var/newlogs]# chattr +c logdata
[root@sysresccd /mnt/root/var/newlogs]# lsattr
--------c---------- ./logdata

Disable copy-on-write per-file / per-folder (+C - capital C = disable copy-on-write / COW)

[root@sysresccd /mnt/myfs]# chattr +C mydata
[root@sysresccd /mnt/myfs]# lsattr
---------------C--- ./mydata

Get Partition UUIDs using lsblk

lsblk -o NAME,PATH,FSTYPE,PARTUUID

NAME                   PATH                         FSTYPE      PARTUUID
loop0                  /dev/loop0                   squashfs
sda                    /dev/sda

├─sda1                 /dev/sda1                    ext4        f2f886a3-69b6-4ea6-87e4-c09e5cd830e4

├─sda14                /dev/sda14                               d1f9156b-8149-4c86-abb4-02319d7859e4

└─sda15                /dev/sda15                   vfat        ce0d08a4-ea60-4f3f-b06d-d61a1d1560ea

sdc                    /dev/sdc

└─sdc1                 /dev/sdc1                    xfs         913b0a09-a337-ac45-93fe-64ab23be14a0

Adding btrfs to /etc/fstab

# Remove the 'compress' option if you don't want automatic compression

LABEL=mydata     /mnt/myfs                btrfs   defaults,noatime,compress   0 0

# Using `subvol=` we can choose to mount a specific subvolume here

LABEL=mydata     /mnt/mydata              btrfs   subvol=/mydata,defaults,noatime,compress   0 0

# You can also use standard /dev/sdx0 notation, or partition UUIDs

/dev/sda3        /mnt/myfs                btrfs   defaults,noatime,compress   0 0

UUID=d1f9156b-8149-4c86-abb4-02319d7859e4   /mnt/myfs     btrfs   defaults,noatime,compress   0 0

Creating, removing, and managing snapshots of btrfs

[root@sysresccd /mnt/myfs]# mkdir snapshots

# Create a snapshot of the subvolume `mydata` into the folder `snapshots/`

[root@sysresccd /mnt/myfs]# btrfs subvolume snapshot /mnt/myfs/mydata /mnt/myfs/snapshots/mydata-2019-08-15

# We can see the snapshots appear as subvolumes of myfs

[root@sysresccd /mnt/myfs]# btrfs subvolume list /mnt/myfs
ID 257 gen 8 top level 5 path mydata
ID 2536 gen 3216 top level 327 path snapshots/mydata-2019-08-15

# To remove a snapshot, just remove it like a subvolume

[root@sysresccd /mnt/myfs]# btrfs subvolume delete /mnt/myfs/snapshots/mydata-2019-08-15

Defragmenting and forcing re-compression of folders/subvolumes

# -v = verbose (print filenames as they're defragged)

# -r = defrag recursively (warning: usually will not descend into subvolumes. you must specify each subvolume individually)

# -clzo = Force re-compress all affected files with LZO while they're defragmented

[root@sysresccd /mnt/myfs]# btrfs filesystem defragment -v -r -clzo /mnt/myfs/mydata