Example tutorial for configuring the bcache module-Linux Operation and Maintenance-php.cn

Example tutorial for configuring the bcache module

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Release： 2017-07-17 11:35:52

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1. Prerequisite: The bcache module needs to be configured in the kernel

##1.1 Check

　-Whether it exists in the kernel: check whether the /sys/fs/bcache directory exists, it does not mean that there is no bcache in the kernel

　-Whether it exists as a kernel module: check /lib/modules/<$version> Does the /kernel/drivers/md/bcache directory exist? If it does not exist, it means that there is no bcache kernel module

- If there is no bcache after checking the above two steps, it means that the kernel is not configured to compile bcache, and you need to configure and compile a new one yourself. Kernel (you need to pay attention to the version when downloading the kernel, the bcache function is only available in 3.10 and above)

1.2 Compile the new kernel

$ wget ""                    $ rpm2cpio ./kernel-3.10.0-514.el7.src.rpm | cpio -idmv    //提取rpm包内容,获取内核：linux-3.10.0-514.el7.tar.xz$ make menuconfig    　　　　//内核配置     Device Drivers 
         ->Multiple devices driver support (RAID and LVM)             -><*> Block device as cache
$ make bzImage (V=1)　　　　 //编译内核$ make modules　　　　　　　　//编译内核模块$ make modules_install      //拷贝内核模块的.ko文件到/lib/modules下$ make install              //拷贝initrd和bzImage到boot目录下，并修改开机启动配置文件$ reboot                    //重启，根据菜单选择对应内核版本进入

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2. Compile and install

//获取bcache-tools工具(以下两个网址任选其一)$ git clone http://evilpiepirate.org/git/bcache-tools.git$ git clone https://github.com/g2p/bcache-tools.git//安装前需要两个依赖包pkg-config和libblkid-dev$ yum -y install pkg-config libblkid-dev//编译安装bcache-tools$ make$ make install

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3. Deployment method

3.1 Create bcache device

$ -bcache -C <cache-device> -B <backing device>--B     -C     -     -b    结果：有几个backing device就会对应生成几个/dev/

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 <br>

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example： the default block and bucket sizes of 512B and 128kB are used. The block size should match the backing devices sector size which will usually be either 512 or 4k . The bucket size should match the erase block size of the caching device with the intent of reducing write amplification. For example, using a HDD with 4k sectors and an SSD with an erase block size of 2MB this command would look like

# make-bcache --block 4k --bucket 2m -C /dev/sdy

##3.2 Add backing device　- 1. Create a back-end device

　　$ make-bcache -B <backing-device>
　　结果：生成对应的设备/dev/bcache<n>

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　- 2. Attach binds the back-end device

　　$  -la /sys/fs/bcache        　　$  <CSET-UUID> > /sys/block/bcache<n>/bcache/

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 <br>

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3.3 Delete the back-end device　- 1 , detach and unbind the backing device

　　$  -la /sys/fs/bcache/        　　$  <CSET-UUID> > /sys/block/bcache<n>/bcache/

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　- 2. Delete the back-end device

　　$   > /sys/block/bcache<N>/bcache/

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3.4 Add caching device

-1. Create caching device

　　$ make-bcache -C <cache device>　　结果：在/sys/fs/bcache目录下生成对应的CACHE SET UUID
　　注意：有可能设备本身有残余数据，需要使用wipefs清理掉
　　$ wipefs -a /dev/sda

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　-2. Attach, associated with bcache device

　　$ echo <CSET-UUID> > /sys/block/bcache<n>/bcache/attach
　　解释：通过后端设备attach缓存设备，cache device才能开始缓存，backing   device才能被缓存

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3.5 Delete the cache device

Prerequisite: Make sure that no backing device is using it (can be viewed through lsblk)Explanation: - The existence of the cache device can be verified through / Understand the cache set uuid corresponding to the sys/fs/bcache directory

- After unregistering the uuid, the cache device is considered deleted

$ echo 1 > /sys/fs/bcache/<cache set uuid>/unregister
结果：再看/sys/fs/bcache目录下就没有这个cache设备的uuid了

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3.6 Format bcache and mount it using

$ mkfs.xfs /dev/bcache<n>            //格式化设备为xfs文件系统$ mount /dev/bcache<n>  /mnt     　　//挂载设备到/mnt目录进行访问

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4. Operation

4.1 Check the running status

$ cat /sys/block/bcache<n>/bcache/state

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no cache: This backing device does not have any caching device attached (meaning all I/O is passed directly to the backing device [pass-through mode]).

clean: everything is ok, the cache is clean.
dirty: This means everything is set up fine and you have writeback enabled, the cache is dirty.
inconsistent: You are encountering a problem because the background device is out of sync with the cache device.

4.2 Check the amount of cached data

$ cat /sys/block/bcache<n>/bcache/dirty_data

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##44.3 View/set cache mode

// 设置缓存模式(默认writethrough)$ echo <cache mode> > /sys/block/bcache<N>/bcache/cache_mode// 查看缓存模式$ cat /sys/block/bcache<N>/bcache/cache_mode
 [writethrough]    writeback        writearound    none

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4.4 Print device information

$ bcache-super-show /dev/sd<n>

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4.5 Configuration information

backing device is in the /sys/block/bcache/bcache/ directory
cache device is in the /sys/fs/bcache// directory

Changes to the configuration information in /sys are temporary Yes, restarting will invalidate it. If you want to set the current configuration at startup, you need to create a conf configuration file in /etc/tmpfile.d/, for example /etc/tmpfile.d/my-bcache.conf:

w /sys/block/bcache0/bcache/sequential_cutoff - - - - 1
w /sys/block/bcache0/bcache/cache_mode - - - - writeback
(To set, in a persistent fashion, the sequential cutoff for bcache0 to 1 MB and write back)

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