clonetab - Man Page

Configuration for dm-clone block devices

Synopsis

/etc/clonetab

Description

The /etc/clonetab file describes dm-clone block devices that are set up during system boot​.

Empty lines and lines starting with the "#" character are ignored​. Each of the remaining lines describes one dm-clone device​. Fields are delimited by white space​.

Each line is in the form

name source-device destination-device metadata-device [options]

The first four fields are mandatory, the fifth is optional​.

The five fields of /etc/clonetab are defined as follows:

  1. The first field contains the name of the resulting dm-clone device; its block device is set up below /dev/mapper/​.
  2. The second field contains a path to the read-only source block device​. This is the device whose data is cloned to the destination device​. Reads to regions not yet hydrated are served directly from this device​.
  3. The third field contains a path to the writable destination block device​. The source device's data is copied here in the background​. It must be at least as large as the source device​.
  4. The fourth field contains a path to the metadata block device​. This small device tracks which regions of the destination have been hydrated and is managed exclusively by dm-clone​.
 5.

The fifth field, if present, contains comma-separated "key=value" options​. The following option is supported:

region-size=BYTES

Controls the granularity of background hydration copying — how much data is copied at a time​. Region size is specified in bytes (standard suffixes like "K", "M", "G" are supported), and must correspond to a power of two between 4 KiB and 1 GiB​. For example, "region-size=4K" or "region-size=4096" sets a 4 KiB region size​.

One region is the atomic unit dm-clone tracks: it is either fully hydrated (copied to the destination) or not, never partially​. If a copy is interrupted mid-region, that whole region is retried from scratch on next boot​. Smaller regions mean finer progress tracking; larger regions reduce metadata overhead​. Defaults to "4K"​. For background, see dm-clone kernel documentation​[1]​.

Added in version 262​.

If no options are needed, the field may be omitted entirely or "-" may be used as a placeholder​.

At early boot and when the system manager configuration is reloaded, this file is translated into native systemd units by systemd-clonesetup-generator(8)​.

Examples

Example ​1. ​Simple clone without options

Clone a source device to a destination, using a separate metadata device:

mydevice /dev/sdb /dev/sdc /dev/sdd

Example ​2. ​Clone with custom region size

Clone a source device to a destination with a custom region size of 8 KiB:

mydevice /dev/sdb /dev/sdc /dev/sdd region-size=8K

See Also

systemd(1), systemd-clonesetup-generator(8), dmsetup(8)

Notes

1.

dm-clone kernel documentation
https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/dm-clone.html

Info

systemd 262~rc2