DASD naming scheme

6.10 LPAR mode z/VM guest KVM guest

The DASD naming scheme maps device names and minor numbers to whole DASDs and to partitions.

The DASD device driver uses the major number 94. For each configured device it uses four minor numbers:

  • The first minor number always represents the device as a whole; including IPL, VTOC, and label records.
  • The remaining three minor numbers represent the up to three partitions.

With 1,048,576 (20-bit) available minor numbers, the DASD device driver can address 262,144 devices.

The DASD device driver uses a device name of the form dasd<x> for each DASD. In the name, <x> is one to four lowercase letters. Table 1 shows how the device names map to the available minor numbers.
Table 1. Mapping of DASD names to minor numbers
Name for device as a whole Minor number for device as a whole Number of devices
From To From To
dasda dasdz 0 100 26
dasdaa dasdzz 104 2804 676
dasdaaa dasdzzz 2808 73108 17,576
dasdaaaa dasdnwtl 73112 1048572 243,866
Total number of devices: 262,144

The DASD device driver also uses a device name for each partition. The name of the partition is the name of the device as a whole with a 1, 2, or 3 appended to identify the first, second, or third partition. The three minor numbers that follow the minor number of the device as a whole are the minor number for the first, second, and third partition.

Examples

  • dasda refers to the whole of the first disk in the system and dasda1, dasda2, and dasda3 to the three partitions. The minor number for the whole device is 0. The minor numbers of the partitions are 1, 2, and 3.
  • dasdz refers to the whole of the 101st disk in the system and dasdz1, dasdz2, and dasdz3 to the three partitions. The minor number for the whole device is 100. The minor numbers of the partitions are 101, 102, and 103.
  • dasdaa refers to the whole of the 102nd disk in the system and dasdaa1, dasdaa2, and dasdaa3 to the three partitions. The minor number for the whole device is 104. The minor numbers of the partitions are 105, 106, and 107.