dmsetup

NAME

dmsetup - low level logical volume management

SYNOPSIS

dmsetup create device_name [-u uuid] [--notable] [table_file]
dmsetup remove device_name
dmsetup remove_all
dmsetup suspend [--nolockfs] device_name
dmsetup resume device_name
dmsetup load device_name [table_file]
dmsetup clear device_name
dmsetup reload device_name [table_file]
dmsetup rename device_name new_name
dmsetup ls [--target target_type] [--exec command] [--tree [-o options]]
dmsetup info [device_name]
dmsetup info -c|-C|--columns [--noheadings] [-o name] [device_name]
dmsetup deps [device_name]
dmsetup status [--target target_type] [device_name]
dmsetup table [--target target_type] [device_name]
dmsetup wait device_name [event_nr]
dmsetup mknodes [device_name]
dmsetup targets
dmsetup version

devmap_name major minor
devmap_name major:minor

DESCRIPTION

dmsetup manages logical devices that use the device-mapper driver. Devices are created by loading a table that specifies a target for each sector (512 bytes) in the logical device.

The first argument to dmsetup is a command. The second argument is the logical device name or uuid.

Invoking the command as devmap_name is equivalent to
dmsetup info -c --noheadings -j major -m minor.

OPTIONS

-c\|-C\|--columns	Display output in columns rather than as Field: Value lines.
-j\|--major major	Specify the major number.
-m\|--minor minor	Specify the minor number.
-n\|--noheadings	Suppress the headings line when using columnar output.
--noopencount	Tell the kernel not to supply the open reference count for the device.
--notable	When creating a device, don’t load any table.
-o\|--options	Specify which fields to display. Only -o name is supported.
-r\|--readonly	Set the table being loaded read-only.
-u\|--uuid	Specify the uuid.
-v\|--verbose	Produce additional output.
--version	Display the library and kernel driver version.

COMMANDS

create	device_name [-u uuid] [--notable] [table_file] Creates a device with the given name. If table_file is supplied, the table is loaded and made live. Otherwise a table is read from standard input unless --notable is used. The optional uuid can be used in place of device_name in subsequent dmsetup commands. If successful a device will appear as /dev/device-mapper/<device-name>. See below for information on the table format.
deps	[device_name] Outputs a list of (major, minor) pairs for devices referenced by the live table for the specified device.
info	[device_name] Outputs some brief information about the device in the form: State: SUSPENDED\|ACTIVE, READ-ONLY Tables present: LIVE and/or INACTIVE Open reference count Last event sequence number (used by wait) Major and minor device number Number of targets in the live table UUID
ls	[--target target_type] [--exec command] [--tree [-o options]] List device names. Optionally only list devices that have at least one target of the specified type. Optionally execute a command for each device. The device name is appended to the supplied command. --tree displays dependencies between devices as a tree. It accepts a comma-separate list of options. Some specify the information displayed against each node: device/nodevice; active, open, rw, uuid. Others specify how the tree is displayed: ascii, utf, vt100; compact, inverted, notrunc.
load\|reload	device_name [table_file] Loads table_file into the inactive table slot for device_name. If table_file is not supplied, reads a table from standard input.
remove	device_name Removes a device. It will no longer be visible to dmsetup and will be deleted when its open_count is zero.
remove_all	Attempts to remove all device definitions i.e. reset the driver. Use with care!
rename	device_name new_name Renames a device.
resume	device_name Un-suspends a device. If an inactive table has been loaded, it becomes live. Postponed I/O then gets re-queued for processing.
status	[--target target_type] [device_name] Outputs status information for each of the device’s targets. With --target, only information relating to the specified target type is displayed.
suspend	[--nolockfs] device_name Suspends a device. Any I/O that has already been mapped by the device but has not yet completed will be flushed. Any further I/O to that device will be postponed for as long as the device is suspended. If there’s a filesystem on the device which supports the operation, an attempt will be made to sync it first unless --nolockfs is specified.
table	[--target target_type] [device_name] Outputs the current table for the device in a format that can be fed back in using the create or load commands. With --target, only information relating to the specified target type is displayed.
targets	Displays the names and versions of the currently-loaded targets.
version	Outputs version information.
wait	device_name [event_nr] Sleeps until the event counter for device_name exceeds event_nr. Use -v to see the event number returned. To wait until the next event is triggered, use info to find the last event number.

TABLE FORMAT

Each line of the table specifies a single target and is of the form:
logical_start_sector num_sectors target_type target_args

There are currently three simple target types available together with more complex optional ones that implement snapshots and mirrors.

linear	destination_device start_sector The traditional linear mapping.
striped	num_stripes chunk_size [destination start_sector]+ Creates a striped area. e.g. striped 2 32 /dev/hda1 0 /dev/hdb1 0 will map the first chunk (16k) as follows: LV chunk 1 -> hda1, chunk 1 LV chunk 2 -> hdb1, chunk 1 LV chunk 3 -> hda1, chunk 2 LV chunk 4 -> hdb1, chunk 2 etc.
error	Errors any I/O that goes to this area. Useful for testing or for creating devices with holes in them.

EXAMPLES

# A table to join two disks together
0 1028160 linear /dev/hda 0
1028160 3903762 linear /dev/hdb 0

# A table to stripe across the two disks,
# and add the spare space from
# hdb to the back of the volume

0 2056320 striped 2 32 /dev/hda 0 /dev/hdb 0
2056320 2875602 linear /dev/hdb 1028160

AUTHORS

Original version: Joe Thornber (thornber@sistina.com)