Time Machine says there "isn't enough space" to back up 2 TB computer on 4 TB external SSD

[alexcr]

I have a SanDisk Extreme Pro Portable SSD with 4 TB capacity that's hooked up to my MacBook Pro 2018, whose internal hard drive is 2 TB.

When I initially set up the external drive, backing up my computer to it worked without issue, maybe for about a week.

But then I started getting regular error messages from Time Machine that backups weren't being completed because there wasn't enough space on the drive.

This makes little sense. When I look at the drive on Finder, for example, is shows only 1.38 TB of storage being used, and there is nothing else on the drive besides Time Machine backups. With that said, when I look a the drive using Disk Utility, it does show the drive as being nearly full, though again, I'm not sure why.

I got in touch with Apple Support regarding this issue. They suggested to me that the external drive must be corrupt, so I went through the trouble of contacting SanDisk and having the drive replaced. That did not resolve the issue; after setting up the new drive, this problem started happening again within about a week.

Does anyone have any idea what might be going on here, and how to resolve it?

(In case it's helpful, the drive is formatted using APFS. I'm using the latest version of Mac OS.)

 

[BrianBaughn]

Do you use OneDrive?

 

[alexcr]

Do you use OneDrive?

I use Windows and Office 365 via Parallels, and that has OneDrive, though I don't really use it much.

 

[gilby101]

Have you excluded your Parallels virtual machines from TM backup? If not, that is the explanation.

 

[zarmanto]

4TB external SSD? How much did you pay for that beast?

 

[alexcr]

4TB external SSD? How much did you pay for that beast?

Here it is...

SanDisk 4TB Extreme PRO Portable SSD - Up to 2000MB/s - USB-C, USB 3.2 Gen 2x2, IP65 Water and Dust Resistance, Updated Firmware - External Solid State Drive - SDSSDE81-4T00-G25

Creating top-tier content can put a strain on your device, your camera or your system. From the brand trusted by professional photographers worldwide, the SanDisk Extreme PRO Portable SSD provides powerful solid state performance featuring 2000MB/s read and 2000MB/s write speeds in a rugged stora...

www.amazon.com

Thanks all for potentially helping me to get to the bottom of this!