This hard drive from Transcend has room for 4 TB of data. The form factor is 2.5" which apart from this model is commonly used in SSD drives.
From Amazon
Transcend 4TB StoreJet 25M3S USB 3.1 Portable Hard Drive Rugged, Anti-Shock Resistant, Compact and Lightweight with Lightning-Fast Speeds and a One Touch Backup Button (Iron Grey) TS4TSJ25M3S
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