If you want to reduce the backup image size of your ps3 partition, you can format the drive and select to have only 10GB reserved for PS3 data. The remaining space will be available for otheros (this is another story).
Now you have a 10GB partition and you can backup it and restore it using dd with size > 10GB. Personally I am using the linux dd command line tool. Another choice is partimage which is providing a good GUI and partition selection.