xm block-list Device Numbers

Virtual devices are named internally in Xen using the Linux-style major and minor numbers. This is true even for non-Linux virtual machines. The number returned from xm block-list is a decimal representation of the combined major and minor numbers.

For example, if a virtual machine’s virtual disk is designated as hda, the number returned from xm block-list is 768. hda has major number 3 and minor number 0. The major number is stored as a high-order byte; the minor is the lower byte. A decimal representation is (3*256)+0 = 768. Another example, sda3 has major number 8 and minor number 3, so its decimal representation is (8*256)+3 = 2051.

Of course, it is possible to manually work backwards from a number to discover the human-readable device name. For your reference, some common mappings listed in the following table.

/dev/hda    768
/dev/hdb    832
/dev/hdc    5632
/dev/hdd    5696
/dev/sda    2048
/dev/sdb    2064
/dev/sdc    2080
/dev/sdd    2096
/dev/xvda   51712
/dev/xvdb   51728
/dev/xvdc   51744
/dev/xvdd   51760