(253,3) are the major and minor number of the fourth LVM Logical Volume that you created.
The explanation that I've seen is that the major number is associated with a software driver for a certain type of device and the minor numbers represent the actual devices under it.
(If you Google "linux major device numbers" you can see quite a few articles trying to explain it. It's a simple concept, but few of these articles give a simple explanation, and I can't either...)
If you cat /proc/devices you can see under the block devices (disks are block devices) that '8' is 'sd' (scsi device) and '253' is device-mapper (which LVM uses -- see the Wikipedia article on "device mapper").
Your real /dev/sda device is probably 8,0; /dev/sda1 is probably 8,1; etc. While your LVM logical volumes are 253,nn.
If you had a hardware RAID array controller, you'd have a different major number and different names for the devices.)
Here is a display from a simple home x86 machine with IDE drives, software RAID (MD devices), and LVM2. You can see the major and minor numbers with an 'ls -l'.
Code:
[root@athlonz ~]# ls -l /dev/sd*
brw-rw---- 1 root disk 8, 0 2009-07-28 12:40 /dev/sda
brw-rw---- 1 root disk 8, 1 2009-07-28 12:41 /dev/sda1
brw-rw---- 1 root disk 8, 2 2009-07-28 12:40 /dev/sda2
brw-rw---- 1 root disk 8, 3 2009-07-28 12:40 /dev/sda3
brw-rw---- 1 root disk 8, 5 2009-07-28 12:40 /dev/sda5
brw-rw---- 1 root disk 8, 16 2009-07-28 12:40 /dev/sdb
brw-rw---- 1 root disk 8, 17 2009-07-28 12:41 /dev/sdb1
brw-rw---- 1 root disk 8, 18 2009-07-28 12:40 /dev/sdb2
brw-rw---- 1 root disk 8, 19 2009-07-28 12:40 /dev/sdb3
brw-rw---- 1 root disk 8, 21 2009-07-28 12:40 /dev/sdb5
[root@athlonz ~]# ls -l /dev/md*
brw-rw---- 1 root disk 9, 0 2009-07-28 12:40 /dev/md0
brw-rw---- 1 root disk 9, 1 2009-07-28 12:41 /dev/md1
[root@athlonz ~]# ls -l /dev/mapper/*
crw-rw---- 1 root root 10, 60 2009-07-28 12:40 /dev/mapper/control
brw-rw---- 1 root disk 253, 1 2009-07-28 12:40 /dev/mapper/vgz00-lvz00
brw-rw---- 1 root disk 253, 0 2009-07-28 12:41 /dev/mapper/vgz00-lvz01
brw-rw---- 1 root disk 253, 3 2009-07-28 12:41 /dev/mapper/vgz01-hfsplus
brw-rw---- 1 root disk 253, 2 2009-07-28 12:41 /dev/mapper/vgz01-lvz00
brw-rw---- 1 root disk 253, 4 2009-07-28 12:41 /dev/mapper/vgz01-maclv
brw-rw---- 1 root disk 253, 5 2009-07-28 12:41 /dev/mapper/vgz01-t
And to make it more interesting, more than one device name can have the same major/minor numbers and therefore represent the same device.
Code:
[root@athlonz ~]# ls -l /dev/root
brw------- 1 root root 253, 0 2009-07-28 12:40 /dev/root
[root@athlonz ~]# ls -l /dev/dm-0
brw-rw---- 1 root disk 253, 0 2009-07-28 12:40 /dev/dm-0
[root@athlonz ~]# ls -l /dev/mapper/vgz00-lvz01
brw-rw---- 1 root disk 253, 0 2009-07-28 12:41 /dev/mapper/vgz00-lvz01
Hope that helps.