14.2.2.3. Using Raw Disk Partitions for the Shared Tablespace

You can use raw disk partitions as data files in the InnoDB system tablespace. This technique enables nonbuffered I/O on Windows and on some Linux and Unix systems without file system overhead. Perform tests with and without raw partitions to verify whether this change actually improves performance on your system.

When you create a new data file, put the keyword newraw immediately after the data file size in innodb_data_file_path. The partition must be at least as large as the size that you specify. Note that 1MB in InnoDB is 1024 × 1024 bytes, whereas 1MB in disk specifications usually means 1,000,000 bytes.

[mysqld]innodb_data_home_dir=innodb_data_file_path=/dev/hdd1:3Gnewraw;/dev/hdd2:2Gnewraw

The next time you start the server, InnoDB notices the newraw keyword and initializes the new partition. However, do not create or change any InnoDB tables yet. Otherwise, when you next restart the server, InnoDB reinitializes the partition and your changes are lost. (As a safety measure InnoDB prevents users from modifying data when any partition with newraw is specified.)

After InnoDB has initialized the new partition, stop the server, change newraw in the data file specification to raw:

[mysqld]innodb_data_home_dir=innodb_data_file_path=/dev/hdd1:3Graw;/dev/hdd2:2Graw

Then restart the server and InnoDB permits changes to be made.

On Windows, you can allocate a disk partition as a data file like this:

[mysqld]innodb_data_home_dir=innodb_data_file_path=//./D::10Gnewraw

The //./ corresponds to the Windows syntax of \\.\ for accessing physical drives.

When you use a raw disk partition, ensure that the user ID that runs the MySQL server has read and write privileges for that partition. For example, if you run the server as the mysql user, the partition must be readable and writeable by mysql. If you run the server with the --memlock option, the server must be run as root, so the partition must be readable and writeable by root.