14.2.3.2. Using Raw Devices for the Shared Tablespace
You can also use raw disk partitions as data files in the shared
tablespace. By using a raw disk, you can perform non-buffered
I/O on Windows and on some Unix systems without filesystem
overhead, which may improve performance.
When you create a new data file, you must 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/hdd1:5Graw;/dev/hdd2:2Graw
Then restart the server and InnoDB allows
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 raw disk partitions, be sure that they have
permissions that allow read and write access by the account used
for running the MySQL server.
