As a new IMAC user, (though I've been using DOS-based computers for 25 years)I felt the need to find a good disk utility package to keep the hard drive working as it should. After doing my homework - comparing software and prices etc, I felt that Drive Genius 2 would meet the need. After finding it, for a great price from an Internet retailer, I bought it about a week ago. After discovering that I would have to boot the computer from the Drive Genius disk, in order to perform the needed tasks on the hard drive, I did so. I then attempted to Defrag the drive, and ran into an immediate problem with the 'catalog btree'. This appeared to be a show-stopper. I attempted to "Repair" the drive, without success. I then sent email to customer support and received excellent results. The problem was specifically explained, and explicit instruction given as to how to fix it. I was told to run "Repair" again, more than once if needed, and if that didn't work to run "Rebuild".
I ran "Rebuild" just once, and things worked as advertised. The btree catalog and the Volume header were restored without any problem. I then defraged the drive, again with great success. There were absolutly no bad sectors on the drive, and this produce is well worth the price. Thanks Prosoft.