btrfs文件系统：CentOS7使用(技术预览版)
Btrfs (读法：B-tree, Butter FS, Better FS),，一种支持写入时复制（COW）的文件系统，运行在Linux作业系统，采用GPL授权。Oracle于2007年对外宣布这项计划，并释出原始码，在2014年8月释出稳定版。目标是取代Linux目前的ext3文件系统，改善ext3的限制，特别是单个文件的大小，总文件系统大小或文件检查和加入ext3未支持的功能。Btrfs也宣称专注在“容错、修复及易于管理”。
核心特性：
- 多物理卷支持：btrfs可由多个底层物理卷组成；支持RAID，以联机“添加”、“移除”，“修改”
- 写时复制更新机制(CoW)：复制、更新及替换指针，而非“就地”更新（直接更新源文件）
- 数据及元数据校验码：checksum
- 子卷：sub_volume
- 快照：支持快照的快照
- 透明压缩
文件系统创建：
mkfs.btrfs
-L 'LABEL'
[root@promote ~]# mkfs.btrfs -L mydata /dev/sdb /dev/sdc
btrfs-progs v4.9.1
See http://btrfs.wiki.kernel.org for more information.
Label: mydata
UUID: f0dd9cf7-d04f-46a0-bec6-2724271a27db
Node size: 16384
Sector size: 4096
Filesystem size: 40.00GiB
Block group profiles:
Data: RAID0 2.00GiB
Metadata: RAID1 1.00GiB
System: RAID1 8.00MiB
SSD detected: no
Incompat features: extref, skinny-metadata
Number of devices: 2
Devices:
ID SIZE PATH
1 20.00GiB /dev/sdb
2 20.00GiB /dev/sdc
[root@promote ~]# blkid /dev/sdb
/dev/sdb: LABEL="mydata" UUID="f0dd9cf7-d04f-46a0-bec6-2724271a27db" UUID_SUB="df6af4ca-61c6-46fe-9a19-5e1270a40433" TYPE="btrfs"
[root@promote ~]# blkid /dev/sdc
/dev/sdc: LABEL="mydata" UUID="f0dd9cf7-d04f-46a0-bec6-2724271a27db" UUID_SUB="9793055b-4f35-449a-8b38-032f762ccfbe" TYPE="btrfs"
-d <type>: raid0, raid1, raid5, raid6, raid10, single
-m <profile>: raid0, raid1, raid5, raid6, raid10, single, dup
-O <feature>
-O list-all: 列出支持的所有feature
[root@centos7 ~]# mkfs.btrfs -O list-all
Filesystem features available:
mixed-bg - mixed data and metadata block groups (0x4, compat=2.6.37, safe=2.6.37)
extref - increased hardlink limit per file to 65536 (0x40, compat=3.7, safe=3.12, default=3.12)
raid56 - raid56 extended format (0x80, compat=3.9)
skinny-metadata - reduced-size metadata extent refs (0x100, compat=3.10, safe=3.18, default=3.18)
no-holes - no explicit hole extents for files (0x200, compat=3.14, safe=4.0)
属性查看：
btrfs filesystem show
[root@promote ~]# btrfs filesystem show
Label: 'mydata' uuid: f0dd9cf7-d04f-46a0-bec6-2724271a27db
Total devices 2 FS bytes used 112.00KiB
devid 1 size 20.00GiB used 2.01GiB path /dev/sdb
devid 2 size 20.00GiB used 2.01GiB path /dev/sdc
[root@promote ~]# btrfs filesystem show /dev/sdb
Label: 'mydata' uuid: f0dd9cf7-d04f-46a0-bec6-2724271a27db
Total devices 2 FS bytes used 112.00KiB
devid 1 size 20.00GiB used 2.01GiB path /dev/sdb
devid 2 size 20.00GiB used 2.01GiB path /dev/sdc
[root@promote ~]# btrfs filesystem label /dev/sdb
mydata
挂载文件系统：
mount -t btrfs /dev/sdb MOUNT_POINT
[root@promote ~]# mkdir /mydata
[root@promote ~]# mount -t btrfs /dev/sdb /mydata
[root@promote ~]# mount
/dev/sdb on /mydata type btrfs (rw,relatime,seclabel,space_cache,subvolid=5,subvol=/)
透明压缩机制：
mount -o compress={lzo|zlib} DEVICE MOUNT_POINT
[root@promote ~]# mount -o compress=lzo /dev/sdb /mydata
[root@promote ~]# cp /etc/rc.d/init.d/functions /mydata/
[root@promote ~]# cd /mydata/
[root@promote mydata]# ll -l
total 28
-rw-r--r--. 1 root root 0 Apr 14 09:58 a.txt
-rw-r--r--. 1 root root 18281 Apr 14 10:02 functions
-rw-r--r--. 1 root root 4335 Apr 14 09:58 grub2.cfg
缩小或增加文件系统
btrfs filesystem resize [+|-] SIZE MOUNT_POINT
[root@promote ~]# btrfs filesystem resize -10G /mydata
Resize '/mydata' of '-10G'
[root@promote ~]# btrfs filesystem show /mydata/
Label: 'mydata' uuid: f0dd9cf7-d04f-46a0-bec6-2724271a27db
Total devices 2 FS bytes used 916.00KiB
devid 1 size 10.00GiB used 2.01GiB path /dev/sdb
devid 2 size 20.00GiB used 2.01GiB path /dev/sdc
[root@promote ~]# df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_promote-root 50G 1.1G 49G 3% /
devtmpfs 898M 0 898M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 9.6M 901M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 1014M 146M 869M 15% /boot
/dev/mapper/centos_promote-home 67G 33M 67G 1% /home
tmpfs 182M 0 182M 0% /run/user/0
/dev/sdb 30G 18M 18G 1% /mydata
添加设备
btrfs device add DEVICE MOUNT_POINT
[root@promote ~]# btrfs device add /dev/sdd /mydata
[root@promote ~]# df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_promote-root 50G 1.1G 49G 3% /
devtmpfs 898M 0 898M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 9.6M 901M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 1014M 146M 869M 15% /boot
/dev/mapper/centos_promote-home 67G 33M 67G 1% /home
tmpfs 182M 0 182M 0% /run/user/0
/dev/sdb 55G 18M 51G 1% /mydata
均衡操作
把/mydata中其它的数据，均衡（移动到）到新添加的磁盘中（会占用io资源）
[root@promote ~]# btrfs balance start /mydata
注意：如果数据量过大的时候，这个时间可能就会很久
balance也有暂停（pause），继续（resume），取消（cancel）等操作，可以通过man btrfs-balance去查看下
移除一个物理卷（btrfs会自动把数据先挪走再拆除）：
[root@promote ~]# btrfs device delete /dev/sdb /mydata
[root@promote ~]# df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_promote-root 50G 1.1G 49G 3% /
devtmpfs 898M 0 898M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 9.6M 901M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 1014M 146M 869M 15% /boot
/dev/mapper/centos_promote-home 67G 33M 67G 1% /home
tmpfs 182M 0 182M 0% /run/user/0
/dev/sdc 40G 18M 38G 1% /mydata
[root@promote ~]# btrfs filesystem show /mydata/
Label: 'mydata' uuid: f0dd9cf7-d04f-46a0-bec6-2724271a27db
Total devices 2 FS bytes used 916.00KiB
devid 2 size 20.00GiB used 2.03GiB path /dev/sdc
devid 3 size 20.00GiB used 2.03GiB path /dev/sdd
修改raid级别
修改数据的组织机制：act on data chunks
btrfs balance -dconvert=raid0 /mydata
修改元数据的组织机制：act on metadata chunks
btrfs balance -mconvert=raid1 /mydata
修改系统的组织机制：act on system chunks
btrfs balance -sconvert=raid5 /mydata
btrfs的子命令：
filesystem
device
balance
subvolume #子卷的管理命令
创建一个子卷cache：
[root@promote ~]# btrfs subvolume create /mydata/cache
Create subvolume '/mydata/cache'
[root@promote ~]# btrfs subvolume list /mydata
ID 261 gen 50 top level 5 path cache
挂载子卷
[root@promote ~]# umount /mydata
[root@promote ~]# mount -o subvol=cache /dev/sdb /mnt
[root@promote ~]# ls /mnt
messages
[root@promote ~]# btrfs subvolume show /mnt
/mnt
Name: cache
UUID: 027abbea-474f-2c4c-b258-c931b99b47cc
Parent UUID: -
Received UUID: -
Creation time: 2019-04-14 10:31:10 +0800
Subvolume ID: 261
Generation: 51
Gen at creation: 49
Parent ID: 5
Top level ID: 5
Flags: -
Snapshot(s):
也可以使用subid挂载
mount -o subvolid=268 /dev/sdb /mnt
查看volid：
[root@promote ~]# btrfs subvolume list /mydata
ID 261 gen 50 top level 5 path cache
删除子卷（注意：请先挂在父卷）：
[root@promote ~]# btrfs subvolume delete /mydata/cache
Delete subvolume (no-commit): '/mydata/cache'
创建快照(快照卷必须与原卷在同一个卷组中)：
trfs subvolume snapshot /mydata/logs /mydata/logs_snapshot
删除快照：
btrfs subvolume dalete /mydata/logs_snapshot
对单个文件创建快照：
cp --reflink file.txt file.txt_snapshot
把其它文件系统转换成btrfs
这里拿ext4做的测试，其它文件系统请一定要事前严格测试下：
创建一个ext4的文件系统
[root@promote ~]# mke2fs -t ext4 /dev/sdd1
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
327680 inodes, 1310720 blocks
65536 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1342177280
40 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
强制检测下：
[root@promote ~]# fsck -f /dev/sdd1
fsck from util-linux 2.23.2
e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sdd1: 12/327680 files (0.0% non-contiguous), 58463/1310720 blocks
转换(数据没丢):
[root@promote ~]# btrfs-convert /dev/sdd1
create btrfs filesystem:
blocksize: 4096
nodesize: 16384
features: extref, skinny-metadata (default)
creating ext2 image file
creating btrfs metadatacopy inodes [o] [ 0/ 12]
conversion complete[root@promote ~]#
查看有没有生效：
[root@promote ~]# btrfs filesystem show
warning, device 3 is missing
Label: 'mydata' uuid: f0dd9cf7-d04f-46a0-bec6-2724271a27db
Total devices 3 FS bytes used 932.00KiB
devid 2 size 20.00GiB used 2.03GiB path /dev/sdc
devid 4 size 20.00GiB used 0.00B path /dev/sdb
*** Some devices missing
Label: none uuid: 3a407f45-6860-49ed-81bd-8cc1d09238d9
Total devices 1 FS bytes used 228.76MiB
devid 1 size 5.00GiB used 485.78MiB path /dev/sdd1
回滚到之前的文件系统（之前是ext4）：
[root@promote ~]# umount /mnt
[root@promote ~]# btrfs-convert -r /dev/sdd1
rollback complete
查看：
[root@promote ~]# blkid /dev/sdd1
/dev/sdd1: UUID="555c8c51-c040-443a-98c1-e2010a2158ac" TYPE="ext4"
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