OpenCAS 的安装与使用 - HanaTaka2137's Blog

NAS 使用机械硬盘做 RAID 时对小文件的读写性能不佳, 使用一块固态硬盘做缓存可以改善此问题. Linux 自带的磁盘缓存机制大多需要向已有设备写入元数据. 但是我的 RAID 阵列中已经存了不少数据了, 写入元数据会破坏已有的数据, 所以我选择安装 OpenCAS 解决缓存问题.

安装 OpenCAS#

系统要求#

建议使用 DEB 或 RPM 系 Linux. OpenCAS 支持导出为 deb, rpm 等安装包安装. 比 make install 更方便.

不建议使用 Ubuntu 26.04, 截至目前 OpenCAS 不支持 Linux 7.x, 并且无法通过 gcc 15 编译.

编译#

服务器使用 Ubuntu Server 24.04.

克隆仓库并切换到稳定版本:

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git clone https://github.com/Open-CAS/open-cas-linux
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cd open-cas-linux
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git checkout v26.03.2 # 替换为最新稳定版

初始化 submodule:

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git submodule update --init

生成配置并编译:

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sudo apt install make gcc
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./configure
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make -j$(nproc)

配置 MOK 证书(可选)#

在 UEFI 引导并且开启了安全启动的系统上必须生成并信任 MOK 证书才能正常使用 DKMS 编译的系统模块.

验证方式:

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ls /sys/firmware/efi
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# 若成功则为 UEFI 引导
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sudo apt install mokutil
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mokutil --sb-state
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# 若输出 “SecureBoot enabled” 则开启安全启动

若经过验证你的系统确实使用 UEFI 引导且开启了安全启动请展开并进行下面的操作

点击展开折叠内容

OpenCAS 的内核模块需要通过 DKMS 编译安装, 所以需要配置 MOK 证书.

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sudo update-secureboot-policy --new-key

执行后 /var/lib/shim-signed/mok/ 会生成对应的 MOK 密钥.

导入密钥:

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sudo apt install mokutil
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sudo mokutil --import /var/lib/shim-signed/mok/MOK.der

执行时需要设置密码, 随便写一个方便记忆的密码, 之后导入时要用.

完成后重启系统:

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reboot

你会进入一个蓝色的界面

选择 Enroll MOK

Enroll MOK Menu

选择 Continue. 如果需要确认可以选择 View key 0 查看详细信息.

Enroll the Key(s)?

选择 Yes

Input password

输入刚才的密码.

选择 Reboot 重启设备.

导出并安装#

先导出为 deb包

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sudo apt install devscripts debhelper fakeroot dkms dh-dkms libelf-dev
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make deb

完成后 /packages 目录下会出现几个 .deb 文件,使用:

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sudo apt install ./packages/*.deb

安装这些 deb 包并重启系统.

重启后执行

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lsmod | grep cas

若输出信息则安装成功.

配置 OpenCAS#

获取磁盘设备 id#

OpenCAS 只支持使用 by-id 的形式配置磁盘. 首先获取缓存设备与后端设备的 id.

使用:

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ls -l /dev/disk/by-id/ | grep -- 'sda$' # “sda” 替换为你的设备名

获取设备的 id.

输入示例如下:

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lrwxrwxrwx 1 root root  9 Jun  5 22:38 scsi-30000000000000000 -> ../../sda
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lrwxrwxrwx 1 root root  9 Jun  5 22:38 scsi-SATA_WDC_XXXXXXXXXXX-_XXXXXXXXXXXXXXXXXXXX -> ../../sda
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lrwxrwxrwx 1 root root  9 Jun  5 22:38 wwn-0x0000000000000000 -> ../../sda

id 建议使用 scsi-SATA_WDC_XXXXXXXXXXX-_XXXXXXXXXXXXXXXXXXXX, 该 id 只与磁盘本身关联, 与接口无关.

配置缓存#

编辑 /etc/opencas/opencas.conf

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sudo vim /etc/opencas/opencas.conf

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version=19.3.0
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# Version tag has to be first line in this file
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#
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# Open CAS configuration file - for reference on syntax
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# of this file please refer to appropriate documentation
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# NOTES:
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# 1) It is required to specify cache/core device using links in
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# /dev/disk/by-id/, preferably those using device WWN if available:
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#   /dev/disk/by-id/wwn-0x123456789abcdef0
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# Referencing devices via /dev/sd* is prohibited because
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# may result in cache misconfiguration after system reboot
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# due to change(s) in drive order. It is allowed to use /dev/cas*-*
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# as a device path.
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## Caches configuration section
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[caches]
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## Cache ID     Cache device                            Cache mode      Extra fields (optional)
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## Uncomment and edit the below line for cache configuration
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#1              /dev/disk/by-id/nvme-INTEL_SSDP..       WT
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 1 /dev/disk/by-id/<刚才获取的缓存设备的id> <缓存模式>
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## Core devices configuration
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[cores]
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## Cache ID     Core ID         Core device     Extra fields (optional)
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## Uncomment and edit the below line for core configuration
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#1              1               /dev/disk/by-id/wwn-0x123456789abcdef0
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 1 1 /dev/disk/by-id/<刚才获取的后端设备的id>
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## To specify use of the IO Classification file, place content of the following line in the
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## Caches configuration section under Extra fields (optional)
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## ioclass_file=/etc/opencas/ioclass-config.csv
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## If given cache/core pair is especially slow to start up, often doesn't come back
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## up after reboot or you simply don't care if it does and don't want it to have
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## an effect on your boot you can mark cores as lazy to prevent Open CAS from
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## dropping boot to emergency shell because of this core failure. To do this
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## put following line under in Extra fields (optional) section of core config:
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## lazy_startup=true
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## NOTE: This will cause open-cas.service to not wait for marked core while
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## starting up - this option should be used with care to prevent races with
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## other services for devices (e.g. mounts based on FS labels)

缓存模式:

wt (Write-Through) OpenCAS 默认模式, 数据同时写入缓存与后端.
wb (Write-Back) 数据直接写入缓存, 之后后台异步写入后端. (此模式突然断电可能丢失数据, 建议搭配 UPS 使用.)
wa (Write-Around) 如果数据已经在缓存中则同时更新缓存与后端, 如果不在则直接写入后端.
pt (Pass-Through) 完全透传数据. 相当于关闭缓存, 主要用于调试.
wo (Write-Only) 只缓存写入, 不缓存读取.

配置完成后保存并重启.

重启后运行:

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sudo casadm -L

显示类型以下内容则配置成功.

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type    id   disk           status    write policy   device
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cache   1    /dev/sdb       Running   wb             -
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└core   1    /dev/md0       Active    -              /dev/cas1-1

/dev/cas1-1 即为使用 /dev/sdb 做缓存加速后的 /dev/md0, /dev/md0 已有数据原封不动.