USB Drive Setup in Sync, by Platform

One drive, four different connection steps

A USB or external drive works as a source or destination in Sync on every platform, but how you connect it depends on the device. Phones need the OS to recognize the drive as external storage first; Mac and Windows mount it the way they mount any external disk. This covers all four, then the one step that's the same everywhere: adding it in Sync.

What you need

A USB flash drive or external drive, ideally formatted exFAT. It's readable and writable on iOS, Android, Mac and Windows, so the same drive works across every device without reformatting. FAT32 also works but caps individual files at 4GB.
An adapter, on phones that need one. A USB-C phone and a USB-C drive can often connect directly; an older connector on either end needs a small adapter (see each platform below).
The Sync app, to turn the connection into a repeatable task instead of a one-off manual copy.

iPhone and iPad

iPhones and iPads with a USB-C port connect to a USB drive directly, or with a simple USB-C-to-USB-A adapter for older flash drives. Older Lightning devices need a Lightning-to-USB (or USB-3 camera) adapter. Once connected, iOS mounts the drive as external storage in the Files app, the same place an iCloud Drive or a connected server shows up. The full walkthrough, including the Camera Roll limitation, is in How to Copy Files to a USB Drive on iPhone and iPad.

Android

Most Android phones with a USB-C port support USB On-The-Go (OTG), which is what lets them read an external drive at all. Connect a USB-C drive directly, or a USB-A drive through a small USB-C-to-USB-A OTG adapter. Android mounts it as a storage location in your file manager, alongside internal storage and any SD card. If nothing happens when you plug a drive in, try a different cable before assuming the phone doesn't support OTG: a charge-only cable is a common cause. Full details in How to Copy Files to a USB Drive on Android.

Mac

Plug the drive into a free USB port (through an adapter if it's an older connector and your Mac is USB-C only). macOS mounts it automatically, the same as any external disk, and it shows up in Finder and on the desktop. There's no separate pairing step; once it's mounted in Finder, it's visible to Sync.

Windows

Plug the drive into a free USB port. Windows mounts it automatically and assigns it a drive letter, visible in File Explorer. As with Mac, there's no separate pairing step: once Windows shows the drive, Sync can see it too.

Adding it in Sync

Once the drive is mounted by the OS, the Sync side is the same step on every platform:

Open Sync and go to the Drives tab.
Tap or click Add Drive, then choose the USB/external drive option.
Pick the mounted drive from the system picker.
Use it as the source or destination in a Backup, Restore, or any other task, the same as a cloud drive.

How to Copy Files to a USB Drive on iPhone and iPad
How to Copy Files to a USB Drive on Android
Moving Files Between Two Cloud Drives: the equivalent setup for cloud-to-cloud moves instead of USB.

FAQ

Does Sync support USB and external drives on every platform?

Yes. iPhone and iPad, Android, Mac and Windows all connect to USB and external drives. How the drive gets recognized differs by platform (see above), but once it's mounted, adding it in Sync is the same everywhere.

What format should my USB drive use?

exFAT is the safest choice across all four platforms. iOS, Android, Mac and Windows can all read and write it, so the same drive works without reformatting when you move between devices. FAT32 also works but limits individual files to 4GB.

Do I need an adapter?

Only on phones, and only if the connectors don't match. A USB-C phone and a USB-C drive usually connect directly. An iPhone with Lightning needs Apple's Lightning to USB 3 Camera Adapter or an equivalent; a USB-A flash drive on a USB-C Android phone needs a small USB-C-to-USB-A OTG adapter. Mac and Windows just need the right cable or dongle for the physical ports involved.

Why won't my Android phone recognize the USB drive?

The two most common causes are a phone that doesn't support USB OTG, and a cable that only carries power, not data. Try a different cable first: it's the more common fix.

Is USB drive support free in Sync?

No. USB and external drive support is part of Sync's paid upgrade, a subscription or a one-time lifetime purchase. The free tier covers any one drive, ad-supported, with usage limits.

Can I use the same USB drive across all my devices?

Yes, as long as it's formatted exFAT (or FAT32 for smaller individual files). Add it as a drive in Sync separately on each device; the drive itself doesn't need reformatting to move between an iPhone, an Android phone, a Mac and a Windows PC.