bcache使用

1.编译安装
# git clone
安装前需要两个依赖包pkg-config和libblkid-dev
# apt-get install pkg-config libblkid-dev
然后编译
# make
cc -O2 -Wall -g `pkg-config –cflags uuid blkid` make-bcache.c bcache.o `pkg-config –libs uuid blkid` -o make-bcache
cc -O2 -Wall -g `pkg-config –cflags uuid blkid` probe-bcache.c `pkg-config –libs uuid blkid` -o probe-bcache
cc -O2 -Wall -g -std=gnu99 bcache-super-show.c bcache.o `pkg-config –libs uuid` -o bcache-super-show
# make install
install -m0755 make-bcache bcache-super-show /usr/sbin/
install -m0755 probe-bcache bcache-register /lib/udev/
install -m0644 69-bcache.rules /lib/udev/rules.d/
install -T -m0755 initramfs/hook /usr/share/initramfs-tools/hooks/bcache
if [ -d /lib/dracut/modules.d ]; \
then install -D -m0755 dracut/module-setup.sh /lib/dracut/modules.d/90bcache/module-setup.sh; \
fi
install -m0644 — *.8 /usr/share/man/man8/

2.使用方式
2.1 创建bcache设备
命令：make-bcache -C [cache-device] -B [backing-device]
以vde作为缓存盘，vdb和vdc作为后端设备创建bcache设备，有几个后端设备就会生成几个bcache设备。

# make-bcache -C /dev/vde -B /dev/vdb /dev/vdc
UUID: 8941a5d1-074e-4cc6-a6dd-56cb1f65aed3
Set UUID: 7681dbb3-6558-4e60-b062-5fbb648f6665
version: 0
nbuckets: 20480
block_size: 1
bucket_size: 1024
nr_in_set: 1
nr_this_dev: 0
first_bucket: 1
UUID: 9e28d09b-942d-487e-be22-9132063da572
Set UUID: 7681dbb3-6558-4e60-b062-5fbb648f6665
version: 1
block_size: 1
data_offset: 16
UUID: 1bacf83e-2754-4d6a-a964-09e53e6e679f
Set UUID: 7681dbb3-6558-4e60-b062-5fbb648f6665
version: 1
block_size: 1
data_offset: 16
# ls /dev/bcache* -la
brw-rw—T 1 root disk 250, 0 5月 22 17:23 /dev/bcache0
brw-rw—T 1 root disk 250, 1 5月 22 17:23 /dev/bcache1

然后可以使用lsblk查看这些设备的对应关系
# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 254:0 0 20G 0 disk
└─vda1 254:1 0 20G 0 part /
vdb 254:16 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk
vdc 254:32 0 50G 0 disk
└─bcache0 250:0 0 50G 0 disk
vdd 254:48 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vde 254:64 0 10G 0 disk
├─bcache0 250:0 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk

2.2 添加一块后端设备（backing device）
命令：make-bcache -B [backing-device]

# make-bcache -B /dev/vdh
UUID: bd1bc116-6f39-401e-a328-3bc0af4ac8d1
Set UUID: cd86812e-d24c-46da-b949-683969b59575
version: 1
block_size: 1
data_offset: 16
接着看到对应的设备是/dev/bcache3

查看cache set uuid
# ls -la /sys/fs/bcache/
total 0
drwxr-xr-x 3 root root 0 May 22 17:23 .
drwxr-xr-x 6 root root 0 May 22 17:21 ..
drwxr-xr-x 7 root root 0 May 22 17:26 7681dbb3-6558-4e60-b062-5fbb648f6665
–w——- 1 root root 4096 May 22 17:57 register
–w——- 1 root root 4096 May 22 20:44 register_quiet

“attach”后端设备
命令：echo [cache set uuid] > /sys/block/bcache[N]/bcache/attach
attach之后，缓存设备就能够对新加的后端设备缓存数据了。
# echo 7681dbb3-6558-4e60-b062-5fbb648f6665 > /sys/block/bcache3/bcache/attach

添加后使用lsblk查看
# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 254:0 0 20G 0 disk
└─vda1 254:1 0 20G 0 part /
vdb 254:16 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk
vdc 254:32 0 50G 0 disk
└─bcache0 250:0 0 50G 0 disk
vdd 254:48 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vde 254:64 0 10G 0 disk
├─bcache0 250:0 0 50G 0 disk
├─bcache2 250:2 0 50G 0 disk
└─bcache3 250:3 0 30G 0 disk
vdf 254:80 0 10G 0 disk
vdg 254:96 0 20G 0 disk
vdh 254:112 0 30G 0 disk
└─bcache3 250:3 0 30G 0 disk

2.3 删除一块后端设备
1）detach backing device
命令：echo [cache set uuid] > /sys/block/bcache[N]/bcache/detach
detach后端设备后，对应的bcache设备还是存在的，只不过这个bcache设备是无缓存的，查看其状态可以看到是no cache

比如删除bcache3
# echo 7681dbb3-6558-4e60-b062-5fbb648f6665 > /sys/block/bcache3/bcache/detach
# cat /sys/block/bcache3/bcache/state
no cache
# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 254:0 0 20G 0 disk
└─vda1 254:1 0 20G 0 part /
vdb 254:16 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk
vdc 254:32 0 50G 0 disk
└─bcache0 250:0 0 50G 0 disk
vdd 254:48 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vde 254:64 0 10G 0 disk
├─bcache0 250:0 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vdf 254:80 0 10G 0 disk
vdg 254:96 0 20G 0 disk
vdh 254:112 0 30G 0 disk
└─bcache3 250:3 0 30G 0 disk

2)stop backing device
命令：echo 1 > /sys/block/bcache[N]/bcache/stop
detach后端设备后，对应的bcache设备还存在，如果要删除，还需要stop该设备
# echo 1 > /sys/block/bcache3/bcache/stop
# ls /dev/bcache* -la
brw-rw—T 1 root disk 250, 0 May 22 17:51 /dev/bcache0
brw-rw—T 1 root disk 250, 1 May 22 17:54 /dev/bcache1
brw-rw—T 1 root disk 250, 2 May 22 20:42 /dev/bcache2

# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 254:0 0 20G 0 disk
└─vda1 254:1 0 20G 0 part /
vdb 254:16 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk
vdc 254:32 0 50G 0 disk
└─bcache0 250:0 0 50G 0 disk
vdd 254:48 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vde 254:64 0 10G 0 disk
├─bcache0 250:0 0 50G 0 disk
├─bcache1 250:1 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vdf 254:80 0 10G 0 disk
vdg 254:96 0 20G 0 disk
vdh 254:112 0 30G 0 disk

2.4 新增一块缓存设备（caching device）
1）创建cache设备
命令：make-bcache -C [cache device]
有可能对应的设备已经有一些元数据，需要使用wipefs清理掉

# make-bcache -C /dev/vdf
Device /dev/vdf already has a non-bcache superblock, remove it using wipefs and wipefs -a
# wipefs -a /dev/vdf
4 bytes were erased at offset 0x27fff0000 (linux_raid_member)
they were: fc 4e 2b a9
# make-bcache -C /dev/vdf
UUID: 1f8bc71f-0106-4da5-b781-5de7b1517706
Set UUID: 7bfb0d17-b6d0-4fe9-942b-a1c75a0893ab
version: 0
nbuckets: 20480
block_size: 1
bucket_size: 1024
nr_in_set: 1
nr_this_dev: 0
first_bucket: 1

# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 254:0 0 20G 0 disk
└─vda1 254:1 0 20G 0 part /
vdb 254:16 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk
vdc 254:32 0 50G 0 disk
└─bcache0 250:0 0 50G 0 disk
vdd 254:48 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vde 254:64 0 10G 0 disk
├─bcache0 250:0 0 50G 0 disk
├─bcache1 250:1 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vdf 254:80 0 10G 0 disk
vdg 254:96 0 20G 0 disk
vdh 254:112 0 30G 0 disk
└─bcache3 250:3 0 30G 0 disk
nbsram_a 251:0 0 16M 0 disk
nbsram_b 251:16 0 16M 0 disk
nbsram_c 251:32 0 16M 0 disk

# ls /sys/fs/bcache/ -la
total 0
drwxr-xr-x 4 root root 0 May 22 17:23 .
drwxr-xr-x 6 root root 0 May 22 17:21 ..
drwxr-xr-x 7 root root 0 May 22 17:26 7681dbb3-6558-4e60-b062-5fbb648f6665
drwxr-xr-x 7 root root 0 May 22 21:05 7bfb0d17-b6d0-4fe9-942b-a1c75a0893ab
–w——- 1 root root 4096 May 22 17:57 register
–w——- 1 root root 4096 May 22 21:05 register_quiet

2）与bcache设备关联
命令：echo [cache set uuid] > /sys/block/bcache[N]/bcache/attach
缓存设备需要与bcache设备关联后，才能作为对应bcache设备缓存。

# echo 7bfb0d17-b6d0-4fe9-942b-a1c75a0893ab > /sys/block/bcache3/bcache/attach
# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 254:0 0 20G 0 disk
└─vda1 254:1 0 20G 0 part /
vdb 254:16 0 50G 0 disk
└─bcache1 250:1 0 50G 0 disk
vdc 254:32 0 50G 0 disk
└─bcache0 250:0 0 50G 0 disk
vdd 254:48 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vde 254:64 0 10G 0 disk
├─bcache0 250:0 0 50G 0 disk
├─bcache1 250:1 0 50G 0 disk
└─bcache2 250:2 0 50G 0 disk
vdf 254:80 0 10G 0 disk
└─bcache3 250:3 0 30G 0 disk
vdg 254:96 0 20G 0 disk
vdh 254:112 0 30G 0 disk
└─bcache3 250:3 0 30G 0 disk

2.5 删除cache设备
首先确保没有backing device在使用它，上述的“删除一块后端设备”有说明如何设置取消后端设备对缓存设备的使用。
然后可以使用lsblk来查看是否有盘在引用它。
在在/sys/fs/bcache目录下还有对应的cache set uuid，unregister该set uuid后这个cache设备就被视为删除了。
命令：echo 1 > /sys/fs/bcache/[cache set uuid]/unregister

比如vde已经不作为任何设备的缓存盘了，在/sys/fs/bcache目录下有对应的cache set uuid
# ls /sys/fs/bcache/ -la
total 0
drwxr-xr-x 4 root root 0 5月 26 09:07 .
drwxr-xr-x 6 root root 0 5月 26 09:06 ..
drwxr-xr-x 7 root root 0 5月 26 09:07 7681dbb3-6558-4e60-b062-5fbb648f6665
drwxr-xr-x 7 root root 0 5月 26 09:07 7bfb0d17-b6d0-4fe9-942b-a1c75a0893ab
–w——- 1 root root 4096 5月 26 09:07 register
–w——- 1 root root 4096 5月 26 09:06 register_quiet

然后unregister掉该cache设备
#echo 1 > /sys/fs/bcache/7681dbb3-6558-4e60-b062-5fbb648f6665/unregister
然后再看/sys/fs/bcache目录下已经没有这个cache设备的uuid了
# ls /sys/fs/bcache/ -la
total 0
drwxr-xr-x 3 root root 0 5月 26 09:07 .
drwxr-xr-x 6 root root 0 5月 26 09:06 ..
drwxr-xr-x 7 root root 0 5月 26 09:07 7bfb0d17-b6d0-4fe9-942b-a1c75a0893ab
–w——- 1 root root 4096 5月 26 09:07 register
–w——- 1 root root 4096 5月 26 09:06 register_quiet

2.6 参数调节
1）设置缓存模式
命令：echo [cache mode] > /sys/block/bcache[N]/bcache/cache_mode
可以为不同的bcache设备设置不同的缓存策略
并且设置了缓存策略后，机器重启后仍然生效。
另外，机器重启后，bcache设备也能自动重建出来。
bcache还有其他可以调节的参数，这里不作说明，具体参考官方说明。

3.参考资料

http://blog.csdn.net/liumangxiong/article/details/18090043

http://unix.stackexchange.com/questions/115764/how-to-remove-cache-device-from-bcache