ssd – Recover lost disk space (> 270 GB)

This is likely completely expected and normal.

First, when dealing with disk storage space, there are a number of items that you have to take into account which are worth being aware of.

Overall Drive Space:

Your overall available drive space is going to be much lower than the 2TB (or other units advertised), for a variety of reasons, including:

1. Decimal vs binary storage units – because storage drives are advertised in decimal units, your 2TB hard drive actually only has about 1.73 storage space to begin with.
2. A portion of drive space is reserved for the drive firmware
3. A portion of the drive storage is used for the partition maps and other storage overhead.
4. A portion of the drive is reserved for (Over-provisioning) – typically 7% to 28% of the drive. This allows the SSD to load balance the wear and provide backup as sectors become used or if they are marked bad.
5. Space reserved by the system for factory images, such as the Operating system restore partition (used if you reset your computer or rebuild from scratch). This partition is likely covered in your “Other Volumes: 17.88 GB” portion)

Usable Drive Space

Now that we’re left the usable drive space, you’re left with your 3.59 TB, which matches up in the “Available” in both, so there really isn’t any discrepancy here.

The difference you mention is expected, because what you are viewing are two different measurements.

When you select a folder and asking the Finder to tell you the size, it is manually counting up the file sizes for each file within the folder that it sees. Meanwhile, what you are viewing at the drive level, you’re just looking at the drive’s reported status space.

There will be a large discrepancy between those two, because the Finder “Get Info” doesn’t’ count all files – only those that are recognizable to Finder. System files, snapshots, temporary files, etc are not always visible as files to the Finder.

In addition, there are also several files such as cache and journal files that are considered “purgeable”, meaning the space is both used and free at the same time. (To the Finder, these files are free space, but to the drive, they are used. If you view the root entry of the drive, some of these will be listed in parenthesis next to “Available” as “purgeable)

If you are still concerned about your disk space and want to determine what is using it, I would recommend a tool such as DaisyDisk or Disk Inventory X which should help you narrow down what space is being used where (and for what).