My Photo CopyFormat the drive as exFAT. It is the one format that an iPhone, a Mac and a Windows PC can all read and write, and it has no practical limit on file size, so long 4K videos copy without trouble. On iOS 18 and later you can format the drive from the Files app on the iPhone itself; otherwise use Disk Utility on a Mac or File Explorer on Windows. All three are below. Formatting erases the drive, so copy off anything you want to keep first.
Which format, and why
| Format | iPhone | Mac | Windows | Limit worth knowing |
|---|---|---|---|---|
| exFAT | Read and write | Read and write | Read and write | None in practice |
| FAT32 / MS-DOS (FAT) | Read and write | Read and write | Read and write | No single file over 4 GB |
| APFS | Read and write | Read and write | Not without extra software | Apple devices only |
| Mac OS Extended (HFS+) | Readable | Read and write | Not without extra software | Apple devices only |
| NTFS | Can’t write | Read only | Read and write | Not usable for an iPhone backup |
The two that cause most trouble:
- FAT32 is what many small or older sticks come with. It works until you copy a video bigger than 4 GB, and then that file fails. Roughly ten minutes of 4K at 60 fps passes the limit, and 4K ProRes gets there in under a minute. Photos are never that big, so a FAT32 drive can look fine for months before a long video fails to copy.
- NTFS is common on external hard drives sold for Windows. The iPhone can’t write to it at all, so a backup to it will not start.
If you only use Apple devices, APFS is fine too. exFAT is still the simpler choice: the drive keeps working if you ever need to open it on someone else’s Windows laptop or a TV.
How to check the current format
On a Mac, select the drive in Disk Utility and the format is shown under its name. On Windows, right-click the drive in File Explorer and choose Properties; it is listed as File system. The iPhone doesn’t show the format directly, but if a drive appears in Files and you can’t create a folder on it, NTFS is the usual reason.
Format on iPhone (iOS 18 and later)
You don’t need a computer at all if your iPhone runs iOS 18 or later.
- Plug the drive into the iPhone. Older iPhones need Apple’s Lightning to USB 3 Camera Adapter, ideally with a charger in its Lightning port.
- Open the Files app and tap Browse.
- Under Locations, touch and hold the drive’s name.
- Tap Erase.
- Choose ExFAT, type a name for the drive, and tap Erase.
The options offered are APFS, ExFAT and MS-DOS (FAT). MS-DOS (FAT) is FAT32, with the 4 GB limit, so skip it. If Erase is missing from the menu, check the iOS version in Settings → General → About.
Format on a Mac
- Open Disk Utility (in Applications → Utilities, or search with Spotlight).
- Choose View → Show All Devices. This lets you select the whole drive, not just a volume on it, which gives you the partition scheme option.
- In the sidebar, select the drive itself: the top-level entry, usually named after its maker.
- Click Erase.
- Enter a name, set Format to ExFAT and Scheme to GUID Partition Map.
- Click Erase, close the window when it finishes, and eject the drive before unplugging it.
Format on Windows
- Plug in the drive and open File Explorer.
- Right-click the drive under This PC and choose Format.
- Set File system to exFAT. Leave Allocation unit size at the default.
- Type a volume label, tick Quick Format, and click Start.
- Confirm the warning. Eject the drive with Safely Remove Hardware before unplugging it.
Pick exFAT even if FAT32 is offered as the default. The drive will work with the iPhone either way, but FAT32 will fail on large videos later.
Check the drive on your iPhone
Plug the freshly formatted drive into the iPhone, open Files, tap Browse, and it should appear under Locations with the name you gave it. Tap it and try creating a folder; if that works, the iPhone can write to it. If the drive doesn’t appear at all, formatting was probably not the problem: see drive not showing up or “accessory not supported”, which covers power, adapters and cables.
Formatting is not a backup step you repeat. Do it once when the drive is new or in the wrong format. After that, later backups add only new photos and never need the drive wiped.
Next: the backup itself
With an exFAT drive in place, the rest is covered in iPhone USB backup without a computer: choosing what to copy, keeping the app on screen for a long first run, and reading the result. If you are still choosing a drive, which USB drive for iPhone covers size, speed and power.
Put your photos on the drive
My Photo Copy copies your original photos and videos to the exFAT drive in plain dated folders and reads every file back to check it. No computer and no account. The first 250 are free.
