⑴ UDEV 基础

udev 可管理保存在/dev 目录下的文件、文件只有在接入相应设备后才会生成、设备被拔出后自动删除

它还允许用户添加规则、以便修改/dev中默认的名称和权限、规则保存在/etc/udev/rules.d/目录下

⑵ MySQL 绑定裸设备

只有InnoDB可以用裸设备

优点：绕过了文件系统，读写速度会有提高，并且数据会比较安全、同时降低文件系统负担、也改善系统性能

缺点：太安全了，好多备份工具可能没法用、dd可以考虑

下面介绍如何为mysql共享表空间绑定裸设备

㈠ 制作裸设备

# fdisk /dev/sda

==> /dev/sda5

# partprobe

# fdisk -l

# pvcreate /dev/sda5

# vgcreate -s 16M mysqlvg /dev/sda5

# lvcreate -L 90M -n sharespace mysqlvg

# vim /etc/sysconfig/rawdevices

==> /dev/raw/raw1  /dev/mysqlvg/sharespace

# service rawdevices start

# chkconfig rawdevices on

# chown -R mysql:dba /dev/mapper/mysqlvg-sharespace

㈡ 配置MySQL

① 指定newraw属性

innodb_data_home_dir =

innodb_data_file_path = /dev/mapper/mysqlvg-sharespace:60Mnewraw

② 重启mysql服务，待其完成分区初始化工作后，再关闭mysql服务

③ 修改raw属性

innodb_data_home_dir =

innodb_data_file_path = /dev/mapper/mysqlvg-sharespace:60Mraw

④ 重启mysql服务

如果整个系统重启、裸设备的权限会被回收、导致mysql无法开启

官网描述如下：

will fail after the next reboot, if the /dev-tree is dynamically created by, e.g. udev, a MAKEDEV-script or similar.

After reboot, the device will regain its former permission, typically excluding access by mysql.

alert 报警如下：

130719 20:42:43  InnoDB: Operating system error number 13 in a file operation.

InnoDB: The error means mysqld does not have the access rights to

InnoDB: the directory.

InnoDB: File name /dev/mapper/mysqlvg-sharespace

InnoDB: File operation call: 'open'.

InnoDB: Cannot continue operation.

此时可选方案：

1)写个简单的初始化脚本、当重启的时候自动授权

2)配置 udev条目、

[root@odd rules.d]# pwd

/etc/udev/rules.d

[root@odd rules.d]# cat 60-raw.rules

ACTION=="add", KERNEL=="sda5", GROUP=="dba", MODE=="0660", RUN+="/bin/raw /dev/raw/raw1 %N"

[root@odd rules.d]# cat 65-raw-permissions.rules

KERNEL=="sda5", GROUP="dba", MODE="0660"

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