copy-on-write

A copy-on-write operation occurs the first time any data block is modified on the  for a . The data you want to preserve at the point-in-time of the snapshot is stored on the source virtual disk until the    receives a write request for the source virtual disk. Before the write occurs, the data blocks to be modified are copied over to the  for safekeeping.

Because the snapshot repository virtual disk stores copies of the original data in those data blocks, further changes to those data blocks write directly to the source virtual disk without another copy-on-write. And, because the only data blocks that are physically stored in the snapshot repository virtual disk are those that have changed since the time of the snapshot, the snapshot technology uses less disk space than a full physical copy.

For more information, see Introduction to Snapshot Virtual Disks.