Snapshot target

modulename: dm-snapshot.ko

configname: CONFIG_DM_SNAPSHOT

Linux Kernel Configuration
└─>Device Drivers
└─>Multiple devices driver support (RAID and LVM)
└─>Snapshot target
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Allow volume managers to take writable snapshots of a device.

source code: