Typed this out, however, everything got deleted so I'll make it short.

When choosing the destination for the file, HDD Guru says my Seagate 3TB external HDD is only 375.07GB capacity.

On top of this, I just received a write error at 55%, exactly 1TB. HDD Guru says there is not enough space.

Very frustrating as this has been running for over 24 hours.

Any help?

"HDD Guru" is the name of the forum, not the tool.

Your external drive is configured with a sector size of 4KB, whereas your tool appears to assume a sector size of 512 bytes. Therefore your tool thinks that the capacity is 1/8th of the actual capacity, ie 3TB / 8 = 375GB.

You need to use a different, more recent tool.

_________________
A backup a day keeps DR away.

Any suggestions on what tool? Or could I format the external drive with what the tool is assuming?

Seagate provides DiscWizard, a free OEM version of Acronis True Image.

_________________
A backup a day keeps DR away.

What format was the external 3TB HD? I ask because the same thing happened to my 8GB flash drive, which was changed from FAT32/4096 to FAT/512 via a format in another computer. After force-formatting flash device back to FAT32, it's showing 8GB (minus housekeeping).

_________________
"Take care of thy backups and thy restores shall take care of thee." Ben Franklin revisited