redirect-on-write snapshot
also: ROW
A snapshot technique where changes to the original volume are tracked and written to separate storage, while the snapshot presents a frozen view of the data at the moment of creation.
Redirect-on-write (ROW) is a snapshot method used in storage systems like LVM and some filesystems. When a snapshot is created, the original volume and snapshot initially share the same data blocks. When new writes occur on the original volume, the system redirects those writes to new blocks and records the mapping, preserving the snapshot's frozen state.
This differs from copy-on-write (COW), where writes to the snapshot trigger copies. ROW is efficient for scenarios where the original volume continues to change significantly while snapshots remain mostly static.
Example: Create a snapshot of /dev/vg0/data before a risky operation. New writes go to fresh blocks while the snapshot retains the original data. If something fails, you can revert without losing the snapshot.