clonetab — Configuration for dm-clone block devices
/etc/clonetab
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
namesource-devicedestination-devicemetadata-device[options]
The first four fields are mandatory, the fifth is optional.
The five fields of /etc/clonetab are defined as follows:
The first field contains the name of the resulting dm-clone device; its
block device is set up below /dev/mapper/.
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.
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.
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.
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.
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).
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