An improved method and apparatus for quickly and efficiently updating the original
source volume and original target volumes after the original source volume has
become temporarily unavailable. The original target volume is characterized as
a source volume while the original source volume is temporarily unavailable. Transfer
lists of different data blocks are generated. Data blocks not originally found
on a source are copied to the target. Data blocks included on a target that were
not found on the source are removed. By focusing upon specific data blocks, this
technique avoids the use of filer overhead and other computational resources that
would be expended if the entire volume were recopied.
