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13.8. Btrfs

The btrfs utility is a toolbox for managing btrfs filesystems. There are command groups to work with subvolumes, devices, for whole filesystem or other specific actions.

13.8.1. /etc/fstab

[root@netkiller ~]# cat /etc/fstab 

#
# /etc/fstab
# Created by anaconda on Fri Nov 21 18:16:53 2014
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=6634633e-001d-43ba-8fab-202f1df93339 / ext4 defaults,barrier=0 1 1
UUID=786f570d-fe5c-4d5f-832a-c1b0963dd4e6 /srv btrfs defaults 1 1
UUID=786f570d-fe5c-4d5f-832a-c1b0963dd4e6 /var/lib/mongo  btrfs   noatime,nodiratime,subvol=@mongo 0 2
UUID=786f570d-fe5c-4d5f-832a-c1b0963dd4e6 /var/lib/mysql  btrfs   noatime,nodiratime,subvol=@mysql 0 2
UUID=786f570d-fe5c-4d5f-832a-c1b0963dd4e6 /www  btrfs   noatime,nodiratime,subvol=www 0 2
		
[root@netkiller ~]# df -T
Filesystem     Type     1K-blocks    Used Available Use% Mounted on
/dev/vda1      ext4      41151808 4902608  34135768  13% /
devtmpfs       devtmpfs   8127268       0   8127268   0% /dev
tmpfs          tmpfs      8133908       4   8133904   1% /dev/shm
tmpfs          tmpfs      8133908  849468   7284440  11% /run
tmpfs          tmpfs      8133908       0   8133908   0% /sys/fs/cgroup
/dev/vdb1      btrfs    104856576 1404116 101369420   2% /srv
/dev/vdb1      btrfs    104856576 1404116 101369420   2% /var/lib/mongo
/dev/vdb1      btrfs    104856576 1404116 101369420   2% /var/lib/mysql
tmpfs          tmpfs      1626784       0   1626784   0% /run/user/0
/dev/vdb1      btrfs    104856576 1404116 101369420   2% /www
		
[root@netkiller ~]# ll /srv/
total 0
drwxr-xr-x 1 www    www    132 2016-12-08 15:17 apache-tomcat-8.5.8
drwxr-xr-x 1 root   root   132 2016-12-08 16:11 apache-tomcat-www
drwxr-xr-x 1 mongod mongod 608 2016-12-26 09:18 @mongo
drwxr-x--x 1 mysql  mysql  448 2016-12-26 09:16 @mysql
drwxr-xr-x 1 root   root     0 2016-11-30 13:24 @redis
drwxr-xr-x 1 root   root    22 2016-12-08 16:32 sbin
drwxr-xr-x 1 www    www     24 2016-12-08 16:54 www
		

13.8.2. btrfs

yum install btrfs-progs
		
# mkfs.btrfs /dev/sdb1
		

指定卷标

# mkfs.btrfs /dev/sdb2 -L /backup
		

13.8.3. Mount Btrfs

# mkdir /mnt/btrfs
# mount /dev/sdb1 /mnt/btrfs
		

查看挂载是否成功

# df -Th
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/sda1     ext4     49G   15G   32G  32% /
tmpfs        tmpfs     32G  264K   32G   1% /dev/shm
/dev/sda3     ext4     52G  1.3G   48G   3% /var
/dev/sdb1    btrfs    2.0T   14G  2.0T   1% /mnt/btrfs
		
 针对 SSD 的优化:
# mount –t btrfs –o SSD /dev/sda5 /btrfsdisk


打开压缩功能:
# mount –t btrfs –o compress /dev/sda5 /btrfsdisk
		

13.8.3.1. Mount Snap

mount -t btrfs -o subvol=your_snapshot /dev/sdb2 /mnt/snap

mount -t btrfs -o subvol=aaa /dev/md127p5 /mnt/snap
			

13.8.3.2. fstab

13.8.3.2.1. btrfs-show
[root@r610 ~]# btrfs-show
Label: none  uuid: 0b097eeb-1f0b-476a-955b-52122ef42bfc
        Total devices 1 FS bytes used 13.03GB
        devid    1 size 2.00TB used 24.04GB path /dev/sdb1

Btrfs Btrfs v0.19
				
13.8.3.2.2. /etc/fstab
UUID=0b097eeb-1f0b-476a-955b-52122ef42bfc /opt    btrfs   defaults 1 2
				

13.8.4. subvolumes

# df -T
Filesystem     Type  1K-blocks      Used Available Use% Mounted on
/dev/md126p2   ext4   50395844  19952780  27883064  42% /
tmpfs          tmpfs   4024944       800   4024144   1% /dev/shm
/dev/md126p1   ext4     495844    172140    298104  37% /boot
/dev/md126p6   btrfs 500084736 360835636 119893924  76% /opt
/dev/md126p5   btrfs 409600000  24927332 368284612   7% /www

# btrfs subvolume create /www/git
Create subvolume '/www/git'

# btrfs subvolume list /www
ID 641 gen 21351 top level 5 path git
			

fstab 挂在子卷

$ cat /etc/fstab 

#
# /etc/fstab
# Created by anaconda on Thu Oct 18 13:53:45 2012
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=88ec1ccf-7d8d-4107-a143-1ed0ec64a572 /                       ext4    defaults        1 1
UUID=c0786771-1c85-45be-a9ab-ef3ee16fccb4 /boot                   ext4    defaults        1 2
UUID=e1b89740-21f0-4507-97e9-a658cd7d3716 /opt                    btrfs   defaults        1 2
UUID=76e46795-ebaf-4d2d-8996-1e15979bf3c8 /www                    btrfs   defaults        1 2
UUID=76e46795-ebaf-4d2d-8996-1e15979bf3c8 /home/git               btrfs   defaults,subvol=git        1 2
UUID=c578f1b3-4bbe-4f48-b3d3-3929c65cb99c swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
		

13.8.5. snapshot

创建快照
# btrfs subvolume snapshot /www /www/backup_2012
查看快照
# btrfs subvolume list -a /www
挂在快照
# mount -t btrfs -o subvol=backup_2012 /dev/md127p5 /mnt/snap
删除快照
# btrfs subvolume delete /www/backup_2012
Delete subvolume '/www/backup_2012'
		

13.8.6. btrfsctl

13.8.6.1. Resizes the filesystem

13.8.6.2. Snapshot

Btrfs v0.19

# touch /mnt/btrfs/test1
# touch /mnt/btrfs/test2
# ls /mnt/btrfs/test?
/mnt/btrfs/test1  /mnt/btrfs/test2
				
# echo 'This is a test' > /mnt/btrfs/test1
# btrfsctl –s snap1 /mnt/btrfs
#vi test1
 Test1 is modified
#cd /mnt/btrfs/snap1
#cat test1
 This is a test
			

13.8.7. btrfs-vol

# btrfs-vol –a /dev/sdc1 /mnt/btrfs
		

13.8.8. btrfs-convert

btrfs-convert /dev/sdb1
		

13.8.9. btrfsck

# btrfsck /dev/sdb1
found 13994164224 bytes used err is 0
total csum bytes: 13588316
total tree bytes: 79728640
total fs tree bytes: 28860416
btree space waste bytes: 10282024
file data blocks allocated: 13931024384
 referenced 13906980864
Btrfs Btrfs v0.19
		

13.8.10. btrfs-debug-tree

[root@r610 ~]# btrfs-debug-tree /dev/sdb1 |head
root tree
leaf 49463296 items 9 free space 2349 generation 298 owner 1
fs uuid 0b097eeb-1f0b-476a-955b-52122ef42bfc
chunk uuid 2826f868-c775-4835-8690-1020a2a9fbf5
        item 0 key (EXTENT_TREE ROOT_ITEM 0) itemoff 3756 itemsize 239
                root data bytenr 49446912 level 2 dirid 0 refs 1
        item 1 key (DEV_TREE ROOT_ITEM 0) itemoff 3517 itemsize 239
                root data bytenr 36139008 level 0 dirid 0 refs 1
        item 2 key (FS_TREE INODE_REF 6) itemoff 3500 itemsize 17
                inode ref index 0 namelen 7 name: default