Copy-on-Write

A strategy used to optimize the copying of resources. Resources are lazily copied. Only when a write is attempted is the resource copied. Up to that point, only reads have taken place, which do not effect the state of the resource.

Filesystem Copy-on-Write

A strategy for Filesystem Integrity where data blocks are never rewritten, but copied to free space Blocks are rewritten in an order tyhat guarantees that the filesystem is always consistent e.g. ZFS, BTRFS