BinDiff
Helper app for VMware .vmdk files differential backup
...Imagine that you have a VM with 10GB vmdk file that you backup every day. So, you need to keep 100GB (let say 60GB with compression) for 10 days. However from those 10GB file only ~500MB is daily changed and you can shrink your backup storage to 15GB, if you keep only the daily difference. The BinDiff makes this job for you.
Initially you make a full copy of vmfk file (let's say every month or two). That time you also make a hash file to track the block changes. You keep the hash file (which is small enough) and every day make a differential file from vmdk file that you keep on the backup storage. ...