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6.13 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 are 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
6.14 File-Backed Virtual Disks and
Loopback Devices
When a virtual machine is running, each of its file-backed virtual disks consumes a
loopback device on the host. By default, the host allows up to 64 loopback devices to
be consumed.
Virtualization: Configuration Options and Settings
69
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