Disclosed is a method and apparatus for tracking in-progress writes to
a data volume and a copy thereof using a multi-column bit map. The method can be
implemented in a computer system and, in one embodiment, includes creating a data
volume in a first memory, and creating a copy of the data volume in a second memory.
In response to the computer system receiving a request to write first data to the
data volume, the computer system switches the state of first and second bits of
a map entry in a memory device, wherein the state of the first and second bits
are switched using a single write access to the memory device.
