在这篇https://blog.****.net/Agoni_xiao/article/details/82973202讲过如何编译内核生成bcache模块，现在安装bcache-tools搭建测试环境。
一、安装bcache-tools
1.安装依赖libblkid-devel
yum install libblkid-devel -y
2.下载bcache-tools安装
$ git clone https://github.com/g2p/bcache-tools.git
$ cd bcache-tools
$ make && make install验证bcache-tools安装是否正确：在命令行敲bcache按tab键看是否能够联想或者直接输入 make-bcache是否有命令提示
二、搭建bcache
bcache的原理是用高速的SSD盘为后端HHD盘做缓存，当用户有写IO时，先写到前端高速SSD缓存立即返回，当缓存中数据达到水位线时，开始刷到后端HHD盘；当用户有读IO时，先去缓存读，读到便立即返回，未读到便去后端HHD机械盘找，这里会涉及到读命中的概念。
1.先创建后端低速磁盘
make-bcache -B /dev/sda1
创建后，后端磁盘sda的分区sda1下面出现bcache0
2.创建前段高速盘bcache
make-bcache -C /dev/sdb1
3.查看新建的bcache UUID并初始化
cd /sys/fs/bcache
[[email protected]r120 ~]# cd /sys/fs/bcache/
[[email protected] bcache]# ls
8a5c3a4d-9444-4767-84f1-77d71441776d register register_quiet
初始化bcache0
4.查看新建的bcache uuid并将前后端关联
bcache-super-show /dev/sdb1（查看前端）
[[email protected] bcache]# bcache-super-show /dev/sdb1
sb.magic ok
sb.first_sector 8 [match]
sb.csum 93E3593CC63081FB [match]
sb.version 3 [cache device]
dev.label (empty)
dev.uuid 1a1ee81b-d033-415a-8db0-1232508eb8d0
dev.sectors_per_block 1
dev.sectors_per_bucket 1024
dev.cache.first_sector 1024
dev.cache.cache_sectors 104856576
dev.cache.total_sectors 104857600
dev.cache.ordered yes
dev.cache.discard no
dev.cache.pos 0
dev.cache.replacement 0 [lru]
cset.uuid 8a5c3a4d-9444-4767-84f1-77d71441776d
[[email protected] bcache]#
关联前后端
echo "5cb5581e-1372-45dc-8068-4f1bfb9abb5f" > /sys/block/bcache0/bcache/attach
[[email protected] bcache]# echo "8a5c3a4d-9444-4767-84f1-77d71441776d" > /sys/block/bcache0/bcache/attach
[[email protected] bcache]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdb 8:16 0 447.1G 0 disk
└─sdb1 8:17 0 50G 0 part
└─bcache0 252:0 0 500G 0 disk
sda 8:0 0 9.1T 0 disk
└─sda1 8:1 0 500G 0 part
└─bcache0 252:0 0 500G 0 disk
nvme0n1 259:0 0 372.6G 0 disk
├─nvme0n1p1 259:1 0 1G 0 part /boot
└─nvme0n1p2 259:2 0 371.6G 0 part
├─centos-swap 253:1 0 31.4G 0 lvm [SWAP]
├─centos-home 253:2 0 290.2G 0 lvm /home
└─centos-root 253:0 0 50G 0 lvm /
此时前后端盘都有bcache0说明bcache可正常使用
5.bcache参数的设置
bcache的参数配置在/sys/block/bcache0/bcache
[[email protected] bcache]# ls
attach cache_mode //写策略
dev partial_stripes_expensive
sequential_cutoff stats_five_minute stop //停用bcache时使用
writeback_delay writeback_rate
writeback_rate_p_term_inverse
bypass_torture_test clear_stats
dirty_data readahead state
stats_hour stripe_size
writeback_metadata
writeback_rate_debug
writeback_rate_update_seconds
cache detach label
running stats_day stats_total
verify
writeback_percent //水位线 最高40%
writeback_rate_d_term
writeback_running参数修改使用echo，如
[[email protected] bcache]# cat cache_mode
[writethrough] writeback writearound none
[[email protected] bcache]# echo writeback > cache_mode //切换写策略为writeback
[[email protected] bcache]# cat cache_mode
writethrough [writeback] writearound none6.清理bcache
解除前段盘与后端盘的关系：
echo “uuid”> /sys/block/bcache0/bcache/detach
删除后端盘bcache：
echo 1 > /sys/block/bcache0/bcache/stop
删除前端盘bcache:
cd /sys/fs/bcache/ 查看bcache uuid
echo 1 >/sys/fs/bcache/uuid/unregister
注意：重启设备后lsblk如果后端磁盘还存在bcache0的话，执行echo 1 > /sys/block/bcache0/bcache/stop
清理初始化磁盘：
wipefs -a /dev/sda
mkfs.xfs -f /dev/sda
重新分区：fdisk /dev/sda