Alsoft's DiskWarrior is a disk repair utility. Plain and simple. But don't dismiss it as a one-trick pony. When you have a hard drive that otherwise seems beyond repair, this is the utility you want to have. While I have been making this recommendation almost since DiskWarrior debuted back in 1998, a recent incident confirmed that it is just as true today.
In truth, I have had little use for any disk repair utility over the past several years. I certainly hadn't used DiskWarrior. Based on my anecdotal experience, drives and system software are more reliable now than they were years ago. Whereas I could expect to need a disk repair utility at least several times a year back in the 1990's, problems with my drives almost never happen now. Further, if I do need help, I typically start with the First Aid component of Apple's Disk Utility. It has the convenience of being accessible from the Recovery HD partition built-in to recent Macs, helpful for making repairs to a primary startup disk. And First Aid is usually capable of fixing whatever is ailing my drive. If it can't, it typically means either the drive needs to be reformatted or it has a hardware problem and needs to be replaced. End of story.
"So who needs DiskWarrior anymore?" I found myself asking. I found out the answer when the startup drive in my 2009 Mac Pro inexplicably developed a bizarre symptom a few weeks ago. After a system-wide freeze forced me to do a hard restart, I could no longer get my Mac to boot. About 10 seconds after the Apple logo appeared, the Mac shut itself off. And I do mean off. It wasn't merely that the display went black or that the Mac went to sleep. Rather, the Mac powered off just as if I had selected Shut Down. This continued to happen with each restart. It didn't matter if I started up normally or via a Safe Boot.
My first thought was that this was a hardware problem, probably with the power supply. But before going down that road, I attempted a software fix. I restarted while holding down the Option key. Success! The Startup Manager screen appeared. I selected to start from Recovery HD. This too succeeded. From here, I ran Disk Utility's First Aid. It confirmed that the drive had problems, but said they "could not be repaired."
Apparently, I didn't need a new power supply. I was now thinking that I would instead have to reformat the problem drive, as Disk Utility recommended. I had a backup, so I was not in a panic. Still, I would prefer to avoid this time-consuming step. That's when I remembered DiskWarrior. As I had written previously: "DiskWarrior works by completely rebuilding the drive directory rather than attempting to repair an existing one. This is key to why it's often more successful than other utilities (such as Disk Utility)." I wasn't at all confident that this meant that DiskWarrior would fix my drive now. But it seemed worth a try.
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