btrfs 笔记

学习btrfs文件系统笔记.

btrfs 管理模式和标准的文件系统不同。 btrfs 的顶级卷可以理解为存储池，跨越多个设备添加所有的空间到顶级卷。
在顶级卷中可以直接创建目录结构进行使用，但是并不推荐。推荐的方式是在顶级卷下面创建子卷，然后挂载子卷使用，这样可以最大程度的发挥 btrfs 文件系统的高级特性。
子卷可以和标准目录使用 ls 命令输出没有任何差异，为了在更好的区分子卷还是普通目录，在创建子卷的时候使用 @VOLUME_NAME 的格式进行创建。 ^3e41e6

例如：

/mnt/btrfs/ <-- 这一层还是 xfs 文件系统的范围，下面的三个目录都是手动创建的挂载点
|-- docker_data  <-- 在这里挂载 @docker_data
|-- harbor_data  <-- 在这里挂载 @harbor_data
`-- root  <-- 在这里挂载 btrfs top volume， subvolume=/
    |-- @docker_data  <-- 在这里创建 btrfs subvolume @docker_data. subvolume=@docker_data
    `-- @harbor_data  <-- 在这里创建 btrfs subvolume @harbor_data, subvolume=@harbor_data

在 top volume 里面创建 subvolume 挂载到其他位置使用。
实际使用中不管理子卷的时候 top volume 可以不挂载。

配置完成之后，看到的应该是这样的。

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/mnt/btrfs/ <-- 这一层还是 xfs 文件系统的范围
|-- docker_data  <-- 在这里挂载 btrfs subvolume @docker_data
`-- harbor_data  <-- 在这里挂载 btrfs subvolume @harbor_data

查看当前os支持的特性

➤ mkfs.btrfs -O list-all
Filesystem features available:
mixed-bg            - mixed data and metadata block groups (compat=2.6.37, safe=2.6.37)
quota               - hierarchical quota group support (qgroups) (compat=3.4)
extref              - increased hardlink limit per file to 65536 (compat=3.7, safe=3.12, default=3.12)
raid56              - raid56 extended format (compat=3.9)
skinny-metadata     - reduced-size metadata extent refs (compat=3.10, safe=3.18, default=3.18)
no-holes            - no explicit hole extents for files (compat=3.14, safe=4.0, default=5.15)
fst                 - free-space-tree alias
free-space-tree     - free space tree, improved space tracking (space_cache=v2) (compat=4.5, safe=4.9, default=5.15)
raid1c34            - RAID1 with 3 or 4 copies (compat=5.5)
zoned               - support zoned (SMR/ZBC/ZNS) devices (compat=5.12)
bgt                 - block-group-tree alias
block-group-tree    - block group tree, more efficient block group tracking to reduce mount time (compat=6.1)
rst                 - raid-stripe-tree alias
raid-stripe-tree    - raid stripe tree, enhanced file extent tracking (compat=6.7)
squota              - squota support (simple accounting qgroups) (compat=6.7)

创建 Btrfs 卷

单一设备文件系统:

1	mkfs.btrfs -n 64k -m single -d single -L liarlee_test /dev/nvme1n1

多设备文件系统:

1	mkfs.btrfs -d single -m raid1 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1

更改 Btrfs 的 Raid 存储方式

可以将文件系统的冗余方式进行转换, 例如 raid0, raid1, single.
最好在初始的时候就设定好，后面的转换会导致一段时间的IO不可用。

1	btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt

^9c4bbd

创建轻量副本文件

默认情况下 cp 命令的行为是不启用 CoW 特性的, 需要这个参数.

1	cp --reflink source dest

创建 Subvolume 和删除 Subvolume

创建 Subvolume

1 2	btrfs su create @test Create subvolume './@test'

删除 Subvolume

1 2	btrfs su del @test/ Delete subvolume (no-commit): '/mnt/btrfs/root/@test'

挂载 Btrfs 顶级卷

1 2	mkdir /mnt/btrfs/root/ mount -t btrfs /dev/nvme1n1 /mnt/btrfs/root/

挂载 Btrfs 子卷

命令行挂载

1 2	mkdir /mnt/btrfs/test/ mount -t btrfs -o subvol=@test/ /dev/nvme1n1 /mnt/btrfs/test/

写入 fstab

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UUID=519abb44-a6a3-4ed1-b99d-506e9443e73f   /mnt/btrfs/root          btrfs   defaults,compress=zstd,autodefrag,ssd,space_cache=v2,vol=@
UUID=519abb44-a6a3-4ed1-b99d-506e9443e73f   /mnt/btrfs/docker_data   btrfs   defaults,compress=zstd,autodefrag,ssd,space_cache=v2,subvol=@docker_data
UUID=519abb44-a6a3-4ed1-b99d-506e9443e73f   /mnt/btrfs/harbor_data   btrfs   defaults,compress=zstd,autodefrag,ssd,space_cache=v2,subvol=@harbor_data

Btrfs 文件系统碎片整理

1	btrfs filesystem defragment -r /mnt/btrfs/root

Btrfs 文件系统在线检查

1	btrfs scrub start /mnt/btrfs/root

Btrfs 对特定的文件进行压缩

一般来说, 压缩选项是挂载的时候指定的 compress=zstd 执行自动压缩, compress-force=zstd 执行强制压缩. 这会对挂载之后写入的新文件生效, 旧文件是需要手动处理的.

1	btrfs property set <PATH> compression <VALUE>

Btrfs 测试

Read Throughput

[global]
directory=/mnt
ioengine=libaio
direct=1
rw=randread
bs=16M
size=64M
time_based
runtime=20
group_reporting
norandommap
numjobs=1
thread

[job1]
iodepth=2

Read 测试结果

[root@ip-172-31-10-64 fio]# fio ./job1
job1: (g=0): rw=randread, bs=16M-16M/16M-16M/16M-16M, ioengine=libaio, iodepth=2
fio-2.14
Starting 1 thread
job1: Laying out IO file(s) (1 file(s) / 64MB)
Jobs: 1 (f=1): [r(1)] [100.0% done] [256.0MB/0KB/0KB /s] [16/0/0 iops] [eta 00m:00s]
job1: (groupid=0, jobs=1): err= 0: pid=26359: Thu Nov 18 07:59:17 2021
  read : io=5232.0MB, bw=266745KB/s, iops=16, runt= 20085msec
    slat (msec): min=1, max=70, avg=21.39, stdev=23.43
    clat (msec): min=2, max=130, avg=101.29, stdev=31.01
     lat (msec): min=8, max=139, avg=122.68, stdev=24.96
    clat percentiles (msec):
     |  1.00th=[    7],  5.00th=[   60], 10.00th=[   63], 20.00th=[   66],
     | 30.00th=[   93], 40.00th=[  110], 50.00th=[  118], 60.00th=[  120],
     | 70.00th=[  122], 80.00th=[  126], 90.00th=[  127], 95.00th=[  128],
     | 99.00th=[  130], 99.50th=[  131], 99.90th=[  131], 99.95th=[  131],
     | 99.99th=[  131]
    lat (msec) : 4=0.31%, 10=3.36%, 20=0.92%, 50=0.31%, 100=28.75%
    lat (msec) : 250=66.36%
  cpu          : usr=0.04%, sys=3.80%, ctx=994, majf=0, minf=8193
  IO depths    : 1=0.3%, 2=99.7%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=327/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=2

Run status group 0 (all jobs):
   READ: io=5232.0MB, aggrb=266744KB/s, minb=266744KB/s, maxb=266744KB/s, mint=20085msec, maxt=20085msec

Write Throughtput

[global]
directory=/mnt
ioengine=libaio
direct=1
rw=randread
bs=16M
size=64M
time_based
runtime=20
group_reporting
norandommap
numjobs=1
thread

[job1]
iodepth=2

Write 测试结果

[root@ip-172-31-10-64 fio]# fio ./job1
job1: (g=0): rw=randwrite, bs=16M-16M/16M-16M/16M-16M, ioengine=libaio, iodepth=2
fio-2.14
Starting 1 thread
Jobs: 1 (f=1): [w(1)] [100.0% done] [0KB/256.0MB/0KB /s] [0/16/0 iops] [eta 00m:00s]
job1: (groupid=0, jobs=1): err= 0: pid=26385: Thu Nov 18 08:00:56 2021
  write: io=5248.0MB, bw=267987KB/s, iops=16, runt= 20053msec
    slat (msec): min=1, max=67, avg=12.64, stdev=21.62
    clat (msec): min=12, max=141, avg=109.45, stdev=31.98
     lat (msec): min=18, max=142, avg=122.10, stdev=25.25
    clat percentiles (msec):
     |  1.00th=[   16],  5.00th=[   23], 10.00th=[   66], 20.00th=[   72],
     | 30.00th=[  120], 40.00th=[  124], 50.00th=[  126], 60.00th=[  127],
     | 70.00th=[  128], 80.00th=[  130], 90.00th=[  133], 95.00th=[  135],
     | 99.00th=[  139], 99.50th=[  139], 99.90th=[  141], 99.95th=[  141],
     | 99.99th=[  141]
    lat (msec) : 20=4.57%, 50=0.91%, 100=19.21%, 250=75.30%
  cpu          : usr=1.51%, sys=0.82%, ctx=720, majf=0, minf=1
  IO depths    : 1=0.3%, 2=99.7%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=328/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=2

Run status group 0 (all jobs):
  WRITE: io=5248.0MB, aggrb=267987KB/s, minb=267987KB/s, maxb=267987KB/s, mint=20053msec, maxt=20053msec

记录测试结果：

如果是 -d raid0 -m raid1 可以直接将三个EBS IO1 3000IOPS的卷吃满，直接到 9000
如果是 -d raid1 -m raid1 只能达到3000IOPS，但是容量会有冗余。

对比 Xfs 测试

Write Throughput

[root@ip-172-31-10-64 fio]# fio ./job1
job1: (g=0): rw=randwrite, bs=16M-16M/16M-16M/16M-16M, ioengine=libaio, iodepth=2
fio-2.14
Starting 1 thread
job1: Laying out IO file(s) (1 file(s) / 64MB)
Jobs: 1 (f=1): [w(1)] [100.0% done] [0KB/128.0MB/0KB /s] [0/8/0 iops] [eta 00m:00s]
job1: (groupid=0, jobs=1): err= 0: pid=26541: Thu Nov 18 08:04:01 2021
  write: io=2704.0MB, bw=137688KB/s, iops=8, runt= 20110msec
    slat (msec): min=12, max=130, avg=118.63, stdev=24.61
    clat (msec): min=12, max=130, avg=118.91, stdev=23.73
     lat (msec): min=34, max=255, avg=237.54, stdev=47.53
    clat percentiles (msec):
     |  1.00th=[   14],  5.00th=[   32], 10.00th=[  125], 20.00th=[  125],
     | 30.00th=[  125], 40.00th=[  125], 50.00th=[  125], 60.00th=[  126],
     | 70.00th=[  126], 80.00th=[  126], 90.00th=[  126], 95.00th=[  126],
     | 99.00th=[  129], 99.50th=[  131], 99.90th=[  131], 99.95th=[  131],
     | 99.99th=[  131]
    lat (msec) : 20=1.78%, 50=3.55%, 100=0.59%, 250=94.08%
  cpu          : usr=0.74%, sys=0.49%, ctx=2132, majf=0, minf=1
  IO depths    : 1=0.6%, 2=99.4%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=169/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=2

Run status group 0 (all jobs):
  WRITE: io=2704.0MB, aggrb=137687KB/s, minb=137687KB/s, maxb=137687KB/s, mint=20110msec, maxt=20110msec

Disk stats (read/write):
  nvme4n1: ios=0/10699, merge=0/0, ticks=0/720588, in_queue=702508, util=99.40%

Read Throughput

[root@ip-172-31-10-64 fio]# fio ./job1
job1: (g=0): rw=randread, bs=16M-16M/16M-16M/16M-16M, ioengine=libaio, iodepth=2
fio-2.14
Starting 1 thread
Jobs: 1 (f=1): [r(1)] [100.0% done] [128.0MB/0KB/0KB /s] [8/0/0 iops] [eta 00m:00s]
job1: (groupid=0, jobs=1): err= 0: pid=26570: Thu Nov 18 08:05:27 2021
  read : io=2704.0MB, bw=137694KB/s, iops=8, runt= 20109msec
    slat (msec): min=9, max=165, avg=118.64, stdev=25.59
    clat (msec): min=14, max=165, avg=118.93, stdev=24.65
     lat (msec): min=25, max=288, avg=237.57, stdev=46.62
    clat percentiles (msec):
     |  1.00th=[   16],  5.00th=[   57], 10.00th=[  123], 20.00th=[  123],
     | 30.00th=[  124], 40.00th=[  124], 50.00th=[  124], 60.00th=[  124],
     | 70.00th=[  129], 80.00th=[  129], 90.00th=[  129], 95.00th=[  129],
     | 99.00th=[  131], 99.50th=[  165], 99.90th=[  165], 99.95th=[  165],
     | 99.99th=[  165]
    lat (msec) : 20=4.73%, 100=1.78%, 250=93.49%
  cpu          : usr=0.00%, sys=0.59%, ctx=3558, majf=0, minf=8193
  IO depths    : 1=0.6%, 2=99.4%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=169/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=2

Run status group 0 (all jobs):
   READ: io=2704.0MB, aggrb=137694KB/s, minb=137694KB/s, maxb=137694KB/s, mint=20109msec, maxt=20109msec

Disk stats (read/write):
  nvme4n1: ios=10711/1, merge=0/0, ticks=598336/56, in_queue=579492, util=99.49%

slat 表示submission latency，也就是发送这个IO给内核处理的提交时间花费。  （请求抵达内核的时间）
clat 是提交IO请求给内核之后到IO完成之间的时间，不包括submission latency。 （内核到块设备 ——> 请求处理完成的时间）
bw Bandwidth  带宽
READ 读取的速率


### 文件系统快照
#### 创建文件系统快照

申请一个新的 EBS 卷, 挂载到之前的实例上面, 格式化文件系统, 创建新的 BTRFS 文件系统设备: 
```shell
mkfs.btrfs -L btrfs_snapshot_vault -d single -m single -n 16k /dev/nvme3n1

列出所有的subvolume

1	btrfs su li -t .

创建新的磁盘挂载点

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mkdir -pv /mnt/btrfs_snapshot_loc/

mount -v /dev/nvme3n1 /mnt/btrfs_snapshot_loc/

创建子卷只读快照:

1	btrfs su sn -r @harbor_data ".snapshots/harbor_data-2024-05-08-12:46-ro"

在快照的基础上创建增量快照，并发送到另外一个 btrfs 文件系统的设备，例如 USB。

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btrfs send -p ".snapshots/harbor_data-2024-05-08-12:46-ro/" ".snapshots/harbor_data-2024-05-08-13:03-ro/" | btrfs receive /mnt/btrfs_snapshot_loc/

btrfs send -p ".snapshots/harbor_data-2024-05-08-13:03-ro/" ".snapshots/harbor_data-2024-05-08-13:10-ro/" | btrfs receive /mnt/btrfs_snapshot_loc/

^08cd21

查看目录内容, 分析目录内容和大小.
磁盘占用空间实际是 15GB, 总文件大小是 47GB.

╰─>$ ll
total 0
drwxr-xr-x 1 10000 10000 122 May  8 12:53 harbor_data-2024-05-08-12:46-ro/
drwxr-xr-x 1 10000 10000 122 May  8 13:06 harbor_data-2024-05-08-13:03-ro/
drwxr-xr-x 1 10000 10000 122 May  8 13:11 harbor_data-2024-05-08-13:10-ro/

╰─>$ compsize .
Processed 14560 files, 2192 regular extents (6504 refs), 7311 inline.
Type       Perc     Disk Usage   Uncompressed Referenced
TOTAL      100%       15G          15G          47G
none       100%       15G          15G          47G

为 Btrfs 文件系统添加新的磁盘

添加新的磁盘并列出, 这个时候不会自动平衡文件系统容量, 新添加的磁盘使用容量是空的.

1	╰─>$ btrfs device add -f /dev/nvme3n1 /mnt/btrfs/root

进行文件系统再平衡

╰─>$ btrfs balance start --full-balance /mnt/btrfs/root

╰─>$ btrfs balance status .
Balance on '.' is running
37 out of about 46 chunks balanced (38 considered),  20% left

查看平衡之后的文件系统空间使用情况.

╰─>$ btrfs fi us .
Overall:
    Device size:		 300.00GiB
    Device allocated:		  90.06GiB
    Device unallocated:		 209.94GiB
    Device missing:		     0.00B
    Used:			  87.12GiB
    Free (estimated):		 105.56GiB	(min: 105.56GiB)
    Data ratio:			      2.00
    Metadata ratio:		      2.00
    Global reserve:		  49.48MiB	(used: 48.00KiB)

Data,RAID1: Size:44.00GiB, Used:43.41GiB
   /dev/nvme1n1	  21.00GiB
   /dev/nvme2n1	  23.00GiB
   /dev/nvme3n1	  44.00GiB

Metadata,RAID1: Size:1.00GiB, Used:155.47MiB
   /dev/nvme1n1	   1.00GiB
   /dev/nvme3n1	   1.00GiB

System,RAID1: Size:32.00MiB, Used:16.00KiB
   /dev/nvme1n1	  32.00MiB
   /dev/nvme3n1	  32.00MiB

Unallocated:
   /dev/nvme1n1	  27.97GiB
   /dev/nvme2n1	  27.00GiB
   /dev/nvme3n1	 154.97GiB

╰─>$ btrfs device us .
/dev/nvme1n1, ID: 1
   Device size:            50.00GiB
   Device slack:              0.00B
   Data,RAID1:             21.00GiB
   Metadata,RAID1:          1.00GiB
   System,RAID1:           32.00MiB
   Unallocated:            27.97GiB

/dev/nvme2n1, ID: 2
   Device size:            50.00GiB
   Device slack:              0.00B
   Data,RAID1:             23.00GiB
   Unallocated:            27.00GiB

/dev/nvme3n1, ID: 3
   Device size:           200.00GiB
   Device slack:              0.00B
   Data,RAID1:             44.00GiB
   Metadata,RAID1:          1.00GiB
   System,RAID1:           32.00MiB
   Unallocated:           154.97GiB

为 Btrfs 文件系统移除磁盘

使用 btrfs dev delete 指令移除磁盘，之后会自动重新平衡数据。

btrfs dev delete /dev/nvme4n1 .
ERROR: error removing device '/dev/nvme4n1': unable to go below four devices on raid10

btrfs balance start -dconvert=raid0 -mconvert=raid1 /mnt/btrfs/root/
Done, had to relocate 26 out of 26 chunks

btrfs fi us .
Overall:
    Device size:		 800.00GiB
    Device allocated:		 100.12GiB
    Device unallocated:		 699.88GiB
    Device missing:		     0.00B
    Used:			  48.06GiB
    Free (estimated):		 748.42GiB	(min: 398.49GiB)
    Data ratio:			      1.00
    Metadata ratio:		      2.00
    Global reserve:		  66.77MiB	(used: 0.00B)

Data,RAID0: Size:96.00GiB, Used:47.45GiB
   /dev/nvme1n1	  24.00GiB
   /dev/nvme2n1	  24.00GiB
   /dev/nvme3n1	  24.00GiB
   /dev/nvme4n1	  24.00GiB

Metadata,RAID1: Size:2.00GiB, Used:312.45MiB
   /dev/nvme1n1	   1.00GiB
   /dev/nvme2n1	   1.00GiB
   /dev/nvme3n1	   1.00GiB
   /dev/nvme4n1	   1.00GiB

System,RAID1: Size:64.00MiB, Used:16.00KiB
   /dev/nvme1n1	  32.00MiB
   /dev/nvme2n1	  32.00MiB
   /dev/nvme3n1	  32.00MiB
   /dev/nvme4n1	  32.00MiB

Unallocated:
   /dev/nvme1n1	 174.97GiB
   /dev/nvme2n1	 174.97GiB
   /dev/nvme3n1	 174.97GiB
   /dev/nvme4n1	 174.97GiB

btrfs dev remove 设备并不会再平衡数据，所以如果冗余不够的话，可能会丢数据，在设备坏了的时候使用。

btrfs dev remove /dev/nvme3n1 .

btrfs fi us .
Overall:
    Device size:		 400.00GiB
    Device allocated:		  50.06GiB
    Device unallocated:		 349.94GiB
    Device missing:		     0.00B
    Used:			  48.06GiB
    Free (estimated):		 350.48GiB	(min: 175.51GiB)
    Data ratio:			      1.00
    Metadata ratio:		      2.00
    Global reserve:		  67.02MiB	(used: 0.00B)

Data,RAID0: Size:48.00GiB, Used:47.45GiB
   /dev/nvme1n1	  24.00GiB
   /dev/nvme2n1	  24.00GiB

Metadata,RAID1: Size:1.00GiB, Used:312.70MiB
   /dev/nvme1n1	   1.00GiB
   /dev/nvme2n1	   1.00GiB

System,RAID1: Size:32.00MiB, Used:16.00KiB
   /dev/nvme1n1	  32.00MiB
   /dev/nvme2n1	  32.00MiB

Unallocated:
   /dev/nvme1n1	 174.97GiB
   /dev/nvme2n1	 174.97GiB