The dm-table

• The basis for all of the abstractions of the device mapper is the dm-table.
• This table contains a list of devices that comprise a mapping, and a btree (sorted by virtual sector number) showing where each slice of the device is mapped to.
• Each component of the device-mapper (dm-stripe, dm-snap, etc) uses a am-table internally, and configures it based on its requirements.
• When a device-mapper component gets an I/O request, it consults its internal dm-table to see which dm-device to map the request to. This process might repeat recursively until we get to the underlying block devices.

Originally written by guy keren