LVM snapshots capture a block device in time
An LVM snapshot is neither a copy nor a reflink: it is a fixed-size copy-on-write exception store attached to an origin logical volume. lvcreate -s -L 5G -n snap vg/data allocates 5 GiB from the volume group, and the device-mapper snapshot target records the original contents of each origin chunk the first time it is written. Creation is instant whatever the origin’s size, because nothing is copied. ...