First download the Disk Drill file system recovery software for Mac OS X. Installing is as easy as dragging it to your Applications folder and authorizing Disk Drill to scan your Mac. You'll need to enter your administrator password for this. Optionally, drag the Disk Drill application to the Dock for easy access.
When you first open Disk Drill, you will see a list of all drives, memory cards and devices currently connected to your Mac and available for scanning. This is where you will scan your drives for deleted files and attempt a FAT recovery, NTFS recovery, or HFS recovery on your Mac.
Click on the name of a volume to reveal the partitions inside it. Select the one that harbored your deleted files. Scanning techniques that are unavailable due to the nature of the drive will be automatically grayed out.
Mac HFS recovery is easy if you've had Disk Drill's Recovery Vault or Guaranteed Recovery features enabled prior to your data loss. Just click the Recover button and select the Undelete Protected Data option. In mere minutes, Disk Drill will scour its database and present a list of all salvageable files that were deleted while Recovery Vault was active, preserving the original location and filename. It's the best option for Mac HFS recovery, and it's the feature that separates Disk Drill from the pack.
Even if you didn't have these features enabled before your data loss, you can still perform a Deep Scan to look for deleted files and folders. Deep Scan will take a lot longer to complete, but is sure to find every file that can still be saved. On the downside, Deep Scan will not tell you the original name or location of the files.
USB flash drives and external hard drives are likely to run on FAT or FAT32 file systems. Drives with FAT file systems are supported by all of Disk Drill's recovery techniques: Undelete Protected Data, Quick Scan, and Deep Scan. When you need to recover NTFS on your Mac, Quick Scan and Deep Scan can be used, but the Undelete Protected Data option is not available.
For FAT or FAT32 recovery for Mac, try Undelete Protected Data first. It actually works very similarly to Quick Scan, but keeps better track of the deleted files and is able to present results more quickly and reliably. But this option is not available to recover NTFS data with your Mac.
Quick Scan is the second-fastest method for FAT and NTFS recovery, and uses the file system's own logs to quickly present a list of deleted files that might still be undeleted. It's a great way to scan for files that were deleted very recently.
If data protection wasn't enabled, or the files were deleted too long ago to reliably use Quick Scan, Deep Scanning the drive is a final solution. This will take the longest time to complete and won't retain the file names, but it is very thorough in sniffing out deleted files to complete NTFS and FAT recovery on your Mac.
Deep Scan might be the slowest scanning technique that Disk Drill offers, but it's also the most thorough and universal one. Even if your hard drive has been formatted or corrupted, Deep Scan will be able to put together a lot of the files that went missing. Of course, the more damaged your drive, or the more time that has passed, the less likely Disk Drill will be able to save your files and handle an effective FAT, FAT32, NTFS or HFS+ recovery. But Disk Drill Basic is free - so why not give it a try?