You start a backup expecting it to take a few minutes. An hour later, the progress bar has barely moved.
Phone-to-USB backups can be fast — but there's usually one bottleneck slowing everything down, and the fix depends on which one it is. Here are the common causes, roughly in order of how much they slow things down, and what actually helps.
1. Originals are downloading from iCloud
This is usually the biggest factor on iPhone.
With Optimize iPhone Storage on, many of your originals live only in iCloud, with smaller versions on the phone. A real backup needs the originals, so each one has to be downloaded before it can be copied — and that's limited by your internet connection and by Apple, which can limit how quickly originals download for very large libraries. No app can change that.
Photos already stored in full on the phone copy far faster. So a backup can fly through recent photos, then crawl when it reaches older ones whose originals are in iCloud.
What helps: use fast Wi-Fi, start large backups in the evening, and let them run. As a rough guide, 100 GB over a steady 50 Mbps connection is about four and a half hours of downloading. How to back up iCloud Photos to a USB drive covers this in detail.
2. The drive is slow
Not all USB drives are equal. Inexpensive flash drives often have slow write speeds, and many slow down further once you've copied a few gigabytes. A portable SSD keeps up even on long backups.
What helps: for backing up a whole library, a portable SSD is worth the extra cost. How to make a physical backup of your phone photos compares drive types.
3. The connection is USB 2
The phone's port, the cable, and the drive all set a speed limit — and the slowest one wins.
- iPhone: Pro models starting with the iPhone 15 Pro support USB 3 speeds with a USB 3 cable. Other USB-C iPhones, and all Lightning iPhones, run at USB 2 speeds. The cable in the box has typically been USB 2, even with Pro models.
- Android: many flagship phones support USB 3, while many budget phones are USB 2.
- Cables, adapters, and hubs can quietly cap a USB 3 phone and drive at USB 2.
What helps: if your phone supports USB 3, use a USB 3 cable and a USB 3 drive with no adapters in between.
4. Thousands of small files
Copying one large file is faster than copying the same amount of data as thousands of small ones, because each file carries its own overhead. A photo library is exactly that — tens of thousands of individual photos — so even a fast connection won't reach its headline speed.
What helps: nothing to fix here — but it explains why a library backup is slower than copying a single big video.
5. The app keeps pausing
Phones pause apps that aren't on screen. On iPhone, an app that leaves the foreground — because you switched apps or the screen locked — is suspended soon afterwards. A backup that keeps pausing looks like a slow one.
What helps: VaultDrive keeps the screen awake while a backup runs, so the phone doesn't auto-lock. On iOS 26 and later, the backup keeps running even after you switch apps; on earlier versions, keep VaultDrive open during a big backup. On Android, VaultDrive runs in the background with the screen off.
6. The phone is hot or low on battery
Phones slow themselves down when they get hot, and long transfers generate heat. A low battery can also slow things or stop them altogether.
What helps: keep the phone plugged in and somewhere cool — not in the sun or under a pillow. VaultDrive shows a hint if the phone is unplugged and below 20% battery.
7. It's the first backup
The first backup copies your entire library, which is the slow one by definition. Every backup after that only needs to copy what's new.
What helps: do the first backup once, overnight, and then keep up with short regular ones.
How VaultDrive keeps backups as quick as possible
VaultDrive can't make iCloud or a slow drive faster, but it's built so the time you spend is spent copying:
- Later backups take minutes. With Pro, each backup copies only what's new since the last one on that drive.
- It tells you what's in iCloud when it scans your library, so you know how much will need downloading.
- It shows iCloud download progress for each item, so a slow download looks like progress, not a stall.
- The screen stays awake during a backup on iPhone, and it keeps running after you leave the app on iOS 26 and later. On Android it runs in the background with the screen off.
- One slow or failed item doesn't stop the run — it's logged, and the backup carries on.
- It resumes instead of restarting if a long backup is interrupted, so you never pay for the same copying twice.
It's free for up to 200 files or 2 GB per backup, and Pro is a one-time purchase.
Frequently Asked Questions
Why is my phone-to-USB backup so slow?
The most common bottleneck is downloading originals from iCloud, which is limited by your connection and by Apple. After that come slow flash drives, USB 2 connections and cables, very large numbers of small files, and the phone pausing the app in the background. Each has a different fix, so it's worth finding which one applies.
Does the iPhone model affect USB transfer speed?
Yes. Pro models starting with the iPhone 15 Pro support USB 3 speeds when used with a USB 3 cable, while other USB-C iPhones and all Lightning iPhones transfer at USB 2 speeds. The cable that comes in the box has typically been USB 2 even with Pro models.
Is a flash drive or an SSD faster for phone backups?
A portable SSD is usually much faster. Inexpensive flash drives often have slow write speeds, especially when copying large amounts of data, while a portable SSD keeps up even on long backups. For backing up a whole photo library, an SSD is worth the extra cost.
Why is the backup fast at first and then slows down?
Often because it has moved from photos stored on the phone to originals that have to be downloaded from iCloud, which is much slower. Cheap flash drives can also slow down after the first few gigabytes, and a phone that gets warm may slow itself down to cool off.
Do later backups take as long as the first one?
Not with an incremental backup. The first backup copies the whole library and is the slow one. With VaultDrive Pro, later backups copy only what's new since the last run, so a monthly update usually takes minutes.
How long does it take to back up 100 GB of photos to USB?
It depends mostly on whether the photos are on the phone or in iCloud. Photos stored on the phone copy at the speed of the USB connection and drive, often well under an hour for 100 GB on a fast setup. If the originals have to come down from iCloud, the download dominates: 100 GB at 50 Mbps is about four and a half hours.
The short version
A slow phone-to-USB backup usually has one bottleneck: iCloud downloads, a slow flash drive, a USB 2 connection, thousands of small files, or the phone pausing the app.
Use a portable SSD and a USB 3 cable where your phone supports it, keep the phone plugged in and cool, and run the big first backup overnight on Wi-Fi. After that, VaultDrive Pro copies only what's new, so backups take minutes.