DiskWarrior displays a Directory Optimization Index for each drive. Green is good, meaning that the directory is not fragmented. If it's yellow, this suggests that the directory is "not efficient." This is a good time to run DiskWarrior to prevent problems from arising. When it's red, you really need to run DiskWarrior, both to make the directory more efficient, and to fix problems that can become serious.
For serious issues, select a disk in DiskWarrior, press the Option key, and the Rebuild button becomes Rebuild.... Click this, and then check Scavenge to have DiskWarrior recover files.
DiskWarrior can also check files for damage and check drives for their SMART status, even automatically in the background, alerting you to any problems. And it will work with FileVault encrypted drives; click Unlock on the DiskWarrior window and enter your FileVault password so DiskWarrior can read the disk.
I found DiskWarrior 5 to be a bit more finicky than previous versions. There was one disk that it wasn't able to repair, at first. I launched Apple's Disk Utility, using its repair function and it found nothing wrong. I then tried with DiskWarrior again, and it was able to fix the directory problems.
The speed with which DiskWarrior works depends on the type and size of your drive. It took DiskWarrior just five minutes to run through my retina iMac's SSD. When I optimized the directory of my Time Machine drive, however, it took more than an hour, and used about 10GB of RAM. (This is not unusual. The way Time Machine works, any such drive has gazillions of files.) But DiskWarrior 4 was often unable to repair Time Machine drives at all because of the large number of files. Since DiskWarrior 5 uses 64-bit memory addressing, it can now handle such large directories.
DiskWarrior remains the essential tool for maintaining and repairing disk problems. For both preventive maintenance and repair it's a must-have tool.
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