Linux UDEV和为MySQL InnoDB共享表空间配置裸设备
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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