Creating the partitions

Specific system administration is required before raw devices can be enabled and used. The available tools to configure devices depend on the distribution.

Physical disk space needs to be allocated in partitions on the disks where you want to set up raw devices. The physical I/O subsystem can be on either SCSI or EIDE devices.

Creating the partitions can be done with the Linux default fdisk(8) utility. You must have “root” privileges to use the command fdisk. Refer to the fdisk(8) man pages for a complete description of the command.

This example shows how to set up partitions as raw devices, on four SCSI disks in the system—sda, sdb, sdc, and sdd.

Start fdisk on /dev/sdd:

# fdisk /dev/sdd

The system returns:

The number of cylinders for this disk is set to 8683
....
Command (m for help):

Enter “p” to print the current partition lay-out. The output is:

Disk /dev/sdd: 64 heads, 32 sectors, 8683 cylinders
Units = cylinders of 2048 * 512 bytes
Device Boot Start   End   Blocks  Id  System
/dev/sdd1       1  7499  7678960  83  Linux
/dev/sdd2    7500  8012   525312  82  Linux swap
/dev/sdd4    8013  8683   687104   5  Extended

This sample shows the extended partition (sdd4) has 687104 free blocks, starting from 8013 and ending at 8683. The remaining partitions can be assigned later.

The next example assigns an additional partition for raw bound disk I/O:

Use the n command to create a new partition, and enter “l” at this prompt for logical.

Command (m for help):n
Command action
l  logical (5 or over)
p  primary partition (1-4)

Accept the default by pressing Enter on the keyboard when you are prompted:

First cylinder (8013-8683, default 8013):

Accept the default by pressing Enter on the keyboard when you are prompted:

Last cylinder or +size or +sizeM or +sizeK
(8013-8683, default 8683): 8269

Use the t command, enter “5” at this prompt:

Partition number (1-8):5

Enter “60” at this prompt:

Hex code (type L to list codes): 60

The output is:

Changed system type of partition 5 to 60 (Unknown)

Repeat the above steps to create four partitions for raw device I/O.

Verify the setup using p to print the full partition table before writing it out. Make sure that there are no overlapping partitions and the type for the unassigned partitions is Unknown type 60.

The partition table can now be written to disk and you can quit the fdisk(8) utility.