How to Choose an External Hard Drive for Backups

Your laptop has ten years of photos, tax documents and work files on it, and the only copy lives on a single internal drive that could fail tomorrow. Buying an external hard drive for backups is the cheapest insurance you can get, but the shelf is full of confusing labels: HDD, SSD, USB 3.2 Gen 2, rugged, desktop, portable. Pick the wrong one and you either overpay or end up with a drive that dies in the bottom of a bag.

This guide covers what matters, what does not, and how much storage you really need.

How much space an external hard drive for backups needs

Start with numbers, not marketing. Check how much of your internal drive is used. On Windows, open Settings, System, Storage. On a Mac, open About This Mac and then Storage.

A simple rule: buy at least twice the space you currently use, and three times if you plan to keep versioned backups with File History or Time Machine. Versioned backups keep older copies of changed files, which is what saves you when you overwrite a document or a file gets corrupted, and they grow over time.

Photos and video are usually what fill a drive fastest. A phone that shoots 4K video can add 30 to 50 GB a month if you sync it to your computer, so count those folders separately and plan for at least two years of growth.

Price per terabyte drops sharply between 1 TB and 4 TB, so the larger size is often only 30 to 40 dollars more and buys you years of headroom.

HDD or SSD for backup drives

This is the biggest decision, and it depends on how the drive will be used.

Spinning hard drives (HDD)

A portable HDD gives you the most space for the money. Real transfer speeds sit around 100 to 140 MB/s, so a 500 GB first backup takes roughly an hour to an hour and a half. After that, incremental backups only copy changed files and usually finish in a few minutes. The weakness is physical: a spinning drive can be damaged if it is dropped while running.

Solid state drives (SSD)

A portable SSD has no moving parts, so it survives drops and bumps far better. Speeds range from about 400 MB/s on cheaper models to 1,000 MB/s or more on USB 3.2 Gen 2 drives. The same 500 GB backup finishes in under 15 minutes. The cost is roughly double per terabyte compared with an HDD.

If you want more detail on why the speed on the box rarely matches what you see, our explainer on why SSD speed numbers do not match real life breaks it down.

Why the fastest drive is usually the wrong pick

Reviews and spec sheets push speed above everything. For a backup drive, I think that is backwards.

A backup runs in the background, mostly while you are doing something else or asleep. Whether an incremental backup takes 2 minutes or 6 minutes makes almost no difference to your life. What does matter is capacity, because a full backup drive silently stops protecting new files, and reliability over years of occasional use.

So for a drive that lives on a desk and gets plugged in once a week, a 4 TB HDD at around 100 dollars is a better backup than a 1 TB SSD at the same price. Choose an SSD when the drive travels with you every day, or when you need to restore a whole system quickly for work.

Connections, cables and formatting

A few details trip people up after purchase.

• Port type. Check what your computer has. Many recent laptops have only USB-C. Most drives now ship with a USB-C cable and sometimes a USB-A adapter. Avoid cheap third party adapters, which can cause random disconnects mid backup.
• USB version. USB 3.0, 3.1 Gen 1 and 3.2 Gen 1 all mean the same 5 Gbps. For an HDD that is plenty, since the disk itself is the bottleneck.
• Power. Portable drives up to about 5 TB take power over USB. Desktop drives of 6 TB and up need a wall adapter, which is fine on a desk but not in a bag.
• Formatting. Drives often ship formatted as exFAT, which works on both Windows and macOS. For Time Machine, macOS will reformat it to APFS. For Windows File History, NTFS is best. Formatting wipes the drive, so do it before the first backup, not after.

If your laptop is short on ports already, our guide to choosing a USB-C laptop charger also explains the port labels you will see on cables and hubs.

Setting up a backup routine that runs itself

A drive in a drawer protects nothing. The best setup is the one you do not have to remember.

1. On Windows, plug the drive in, open Control Panel, then File History, and turn it on. Set it to save copies every hour and keep them until space is needed.
2. On a Mac, connect the drive and accept the prompt to use it with Time Machine, or go to System Settings, General, Time Machine.
3. Label the drive with the date you started and set a weekly reminder to plug it in if it does not stay connected.
4. Once a month, open a few random files from the backup to confirm they actually restore.

Ideally, follow the 3-2-1 rule: three copies of your data, on two different types of storage, with one kept off site. A second external drive at a relative's home, swapped every month, covers the off site part cheaply.

Drives also wear out. If yours starts clicking, slows to a crawl or disconnects, replace it before it fails. Our wider hardware buying guides cover other parts worth checking at the same time.

Frequently asked questions

How long does an external hard drive last for backups?

A portable HDD used for weekly backups typically lasts three to five years, sometimes longer. SSDs often last longer in practice because they have no moving parts. Plan to replace a backup drive around the five year mark regardless of how it seems.

Should I leave my backup drive plugged in all the time?

Leaving it connected makes automatic backups easier, but it also exposes the drive to ransomware and power surges. A good compromise is to plug it in for a scheduled backup once or twice a week and unplug it afterwards.

Can I use one external drive for backups and extra storage?

You can, but it is risky. If the drive fails, you lose both your backup and the files you only stored there. Keep backup drives for backups only, and use a separate drive for overflow storage.