Two kinds of drive
An external drive is a storage device that plugs into your computer or phone, usually by USB. There are two main kinds.
A hard disk drive (HDD) stores data on spinning magnetic platters read by a moving head. A solid-state drive (SSD) stores data in flash memory chips and has no moving parts. Both work as external drives, and both can hold backups. The differences show up in speed, toughness, capacity per dollar and how they age.
Speed
SSDs are generally much faster than HDDs, especially when working with lots of small files or opening programs from the drive. For a first backup of a large collection, or for editing video directly from a drive, that difference can be noticeable. For a nightly backup that runs while you sleep, speed matters far less.
The connection also affects speed. A fast SSD on a slow port or cable will be limited by that connection, so check that the drive, cable and port are a good match. The way cables and ports are labeled can be confusing, and the guide to cables and ports helps with the naming.
Durability and portability
Because an HDD has moving parts, a drop or hard knock while it is running can damage it. SSDs have no such parts and generally cope better with bumps and vibration, which suits drives that travel in bags. SSDs are also usually smaller and lighter.
Neither type is indestructible. Water, heat, power surges and rough handling can harm either, and a drive kept in a pocket or bag can be lost. Treat any drive as something that will eventually fail.
Capacity and cost
HDDs have historically offered more storage for the money, which makes them popular for large photo and video collections. SSDs tend to cost more per unit of storage, though prices change over time and vary by brand and size. Instead of trusting a rule, compare what you can actually buy at the capacity you need.
To estimate the capacity, add up the data you want to back up and leave room for growth and for older versions. Many people buy a drive at least twice the size of the data they have now. As a hypothetical example, if you have 400 GB of files, a 1 TB drive leaves room for about two and a half times that amount.
Lifespan and reliability
Both types wear out in different ways. HDDs can fail from mechanical wear or shock. SSDs have a limited number of times each memory cell can be rewritten, though for ordinary backup use this limit is rarely a concern. An SSD left unpowered for a very long time may also lose data in some conditions, so a drive stored in a drawer for years is a poor sole copy.
Because of this, an external drive is best used as one copy among several rather than a permanent archive. The reasoning behind keeping multiple copies is explained in the discussion of the backup rule. Watch for the warning signs of failing devices, such as clicking noises, slow transfers, disconnections and file errors, and replace drives before they become unreliable.
Which suits which job
| Job | Often a good fit | Why |
|---|---|---|
| Large home photo and video backup | HDD | Lower cost for big capacity |
| Backup that travels with you | SSD | Smaller, more shock tolerant |
| Working on large files directly | SSD | Faster response |
| Occasional archive copy | Either | Keep a second copy elsewhere |
These are general tendencies, not rules, and your own priorities matter more.
Other things to check
- Power: many portable drives draw power from the port, while some larger HDDs need their own power supply.
- Formatting: a drive may be set up for one operating system. If you use more than one, check that the format works with both.
- Software: some drives include backup software of unknown quality. The tools built into your operating system are often enough.
- Encryption: if the drive holds sensitive material or travels, consider turning on everyday encryption and storing the recovery key safely.
- Warranty: check the length and terms. The explanation of device warranties covers what to look for.
- Phones and tablets: confirm that the connector and format work, if you want to copy from them directly.
Using a drive well
Safely eject the drive before unplugging it so files are not left half-written. Keep it away from heat and moisture, and label it with the date you last backed up. Store it somewhere other than next to your computer if possible, so a single event does not take out both. Finally, test restoring a few files now and then. A drive that looks fine can still contain a damaged backup.