Apple's Core Storage is a logical volume manager, and it has COW features, in particular when using its dmcache-like function to marry an SSD and HDD into a sin

Apple's Core Storage is a logical volume manager, and it has COW features, in particular when using its dmcache-like function to marry an SSD and HDD into a single logical volume. The could conceivably tack on checksums at this level (instead of parity for example). Core Storage volumes are the default since 10.10, in fact as long as you don't already have a Boot Camp'd dual-boot setup, the Yosemite install process converts the main partition to a Core Storage LV in-place.