This section provides information to help you understand naming patterns for devices on Linux.
Special device files are used by kernel drivers to control a device. There can be more than one special device file that maps to the same physical device. For example, in a multipath environment with four paths to the same device, four different device files will map to the same physical device.
The device files are located in the /dev directory and are addressed by a major and minor number pair. Fibre-channel attached devices are managed as SCSI disk devices by the sd driver. Thus, each of the attached storage unit LUNs has a special device file in the Linux directory /dev.
Names without a trailing digit refer to the whole disk, while names with a trailing digit refer to a partition of that whole disk. By convention, SCSI disks have a maximum of 16 minor numbers mapped to a single disk. Thus, for each whole disk, there is a maximum of 15 partitions per disk because one minor number is used to describe the entire disk (for example /dev/sda), and the other 15 minor numbers are used to refer to partitions for that disk (for example /dev/sda1, /dev/sda2, etc). Figure 1 displays the device files for the whole disk /dev/sda, which has a major number of 8 and a minor number of 0, and its 15 partitions.
# ls -l /dev/sda* brw-rw---- 1 root disk 8, 0 May 24 08:09 /dev/sda brw-rw---- 1 root disk 8, 1 May 24 08:09 /dev/sda1 brw-rw---- 1 root disk 8, 10 May 24 08:09 /dev/sda10 brw-rw---- 1 root disk 8, 11 May 24 08:09 /dev/sda11 brw-rw---- 1 root disk 8, 12 May 24 08:09 /dev/sda12 brw-rw---- 1 root disk 8, 13 May 24 08:09 /dev/sda13 brw-rw---- 1 root disk 8, 14 May 24 08:09 /dev/sda14 brw-rw---- 1 root disk 8, 15 May 24 08:09 /dev/sda15 brw-rw---- 1 root disk 8, 2 May 24 08:09 /dev/sda2 brw-rw---- 1 root disk 8, 3 May 24 08:09 /dev/sda3 brw-rw---- 1 root disk 8, 4 May 24 08:09 /dev/sda4 brw-rw---- 1 root disk 8, 5 May 24 08:09 /dev/sda5 brw-rw---- 1 root disk 8, 6 May 24 08:09 /dev/sda6 brw-rw---- 1 root disk 8, 7 May 24 08:09 /dev/sda7 brw-rw---- 1 root disk 8, 8 May 24 08:09 /dev/sda8 brw-rw---- 1 root disk 8, 9 May 24 08:09 /dev/sda9
For Red Hat, the kernel automatically creates the device files for 128 devices. For SUSE, there are only special device files for the first 16 disks. You must create the device files for additional disks by using the mknod command. For 2.6 kernels, the special device files are only created when they are detected and recognized by the kernel. The /proc/partitions file lists all the ‘sd’ devices that are recognized by the SCSI disk driver, including the sd name, major number, minor number, and size of each disk device.
Figure 2 is an example /proc/partitions file.
# cat /proc/partitions major minor #blocks name 8 0 17774160 sda 8 1 1052226 sda1 8 2 208845 sda2 8 3 10490445 sda3 8 16 976576 sdb 8 32 976576 sdc 8 48 976576 sdd 8 64 976576 sde 8 80 976576 sdf 8 96 976576 sdg 8 112 976576 sdh 8 128 976576 sdi 8 144 976576 sdj 8 160 976576 sdk 8 176 976576 sdl 8 192 976576 sdm 8 208 976576 sdn 8 224 976576 sdo 8 240 976576 sdp 65 0 976576 sdq 65 16 1048576 sdr 65 32 1048576 sds 65 48 1048576 sdt 65 64 1048576 sdu 65 80 1048576 sdv 65 96 1048576 sdw 65 112 1048576 sdx 65 128 1048576 sdy 65 144 1048576 sdz 65 160 1048576 sdaa 65 176 1048576 sdab 65 192 1048576 sdac 65 208 1048576 sdad 65 224 1048576 sdae 65 240 1048576 sdaf 66 0 1048576 sdag 66 16 1048576 sdah 66 32 1048576 sdai 66 48 1048576 sdaj 66 64 1048576 sdak 66 80 1048576 sdal 66 96 1048576 sdam 66 112 1048576 sdan 66 128 1048576 sdao 66 144 1048576 sdap 66 160 1048576 sdaq 66 176 1048576 sdar 66 192 1048576 sdas 66 208 1048576 sdat 66 224 1048576 sdau 66 240 1048576 sdav