---

   dmsetup    ( 8 )

---

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

Simple target types and target args include:

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.

zero Returns blocks of zeroes on reads. Any data written is discarded silently. This is a block-device equivalent of the /dev/zero character-device data sink described in null(4).

More complex targets include:

cache Improves performance of a block device (eg, a spindle) by dynamically migrating some of its data to a faster smaller device (eg, an SSD).

crypt Transparent encryption of block devices using the kernel crypto API.

delay Delays reads and/or writes to different devices. Useful for testing.

flakey Creates a similar mapping to the linear target but exhibits unreliable behaviour periodically. Useful for simulating failing devices when testing.

mirror Mirrors data across two or more devices.

multipath Mediates access through multiple paths to the same device.

raid Offers an interface to the kernel's software raid driver, md.

snapshot Supports snapshots of devices.

thin, thin-pool Supports thin provisioning of devices and also provides a better snapshot support.

To find out more about the various targets and their table formats and status lines, please read the files in the Documentation/device-mapper directory in the kernel source tree. (Your distribution might include a copy of this information in the documentation directory for the device-mapper package.)