DMSETUP(8)

MAINTENANCE COMMANDS

DMSETUP(8)

NAME

dmsetup - low level logical volume management

SYNOPSIS

dmsetup help [-c|-C|--columns]

dmsetup create device_name [-u uuid] [--notable | --table <table> | table_file]

dmsetup remove [-f|--force] device_name

dmsetup remove_all [-f|--force]

dmsetup suspend [--nolockfs] [--noflush] device_name

dmsetup resume device_name

dmsetup load device_name [--table <table> | table_file]

dmsetup clear device_name

dmsetup reload device_name [--table <table> | table_file]

dmsetup rename device_name new_name

dmsetup message device_name sector message

dmsetup ls [--target target_type] [--exec command] [--tree [-o options]]

dmsetup info [device_name]

dmsetup info -c|-C|--columns [--noheadings] [--separator separator] [-o fields] [-O|--sort sort_fields] [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

dmsetup setgeometry device_name cyl head sect start

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.

-r|--readonly: Set the table being loaded read-only.

--readahead [+]<sectors>|auto|none: Specify read ahead size in units of sectors. The default value is "auto" which allows the kernel to choose a suitable value automatically. The + prefix lets you specify a minimum value which will not be used if it is smaller than the value chosen by the kernel. "None" is equivalent to specifying zero.

--table <table>: Specify a one-line table directly on the command line.

-u|--uuid: Specify the uuid.

-v|--verbose [-v|--verbose]: Produce additional output.

--version: Display the library and kernel driver version.

COMMANDS

create: device_name [-u uuid] [--notable | --table <table> | table_file]

Creates a device with the given name. If table_file or <table> 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.

help: [-c|-C|--columns]

Outputs a summary of the commands available, optionally including the list of report fields.

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

info: [--noheadings] [--separator separator] [-o fields] [-O|--sort sort_fields] [device_name]

Output you can customise. Fields are comma-separated and chosen from the following list: name, major, minor, attr, open, segments, events, uuid. Attributes are: (L)ive, (I)nactive, (s)uspended, (r)ead-only, read-(w)rite. Precede the list with '+' to append to the default selection of columns instead of replacing it. Precede any sort_field with - for a reverse sort on that column.

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 <table> | table_file]

Loads <table> or table_file into the inactive table slot for device_name. If neither is supplied, reads a table from standard input.

message: device_name sector message

Send message to target. If sector not needed use 0.

mknodes: [device_name]

Ensure that the node in /dev/mapper for device_name is correct. If no device_name is supplied, ensure that all nodes in /dev/mapper correspond to mapped devices currently loaded by the device-mapper kernel driver, adding, changing or removing nodes as necessary.

remove: [-f|--force] device_name

Removes a device. It will no longer be visible to dmsetup. Open devices cannot be removed except with older kernels that contain a version of device-mapper prior to 4.8.0. In this case the device will be deleted when its open_count drops to zero. From version 4.8.0 onwards, if a device can't be removed because an uninterruptible process is waiting for I/O to return from it, adding --force will replace the table with one that fails all I/O, which might allow the process to be killed.

remove_all: [-f|--force]

Attempts to remove all device definitions i.e. reset the driver. Use with care! From version 4.8.0 onwards, if devices can't be removed because uninterruptible processess are waiting for I/O to return from them, adding --force will replace the table with one that fails all I/O, which might allow the process to be killed. This also runs mknodes afterwards.

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.

setgeometry: device_name cyl head sect start

Sets the device geometry to C/H/S.

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] [--noflush] 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. Some targets such as recent (October 2006) versions of multipath may support the --noflush option. This lets outstanding I/O that has not yet reached the device to remain unflushed.

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

ENVIRONMENT VARIABLES

DM_DEV_DIR: The device directory name. Defaults to "/dev" and must be an absolute path.

AUTHORS

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