NAS vs External Hard Drive: Which Should You Buy?

NAS vs external hard drive: the short answer

An external hard drive is the simple, cheap answer when one computer needs more space or a backup target. It plugs into USB, needs no setup, and portable models run on USB power alone. If the problem is "my laptop is full," this is the tool.

A NAS (network-attached storage) is for shared, always-on storage. Many devices reach it over the network at once, it can run backups and media servers around the clock, it supports remote access, and with RAID it can survive a drive failure without losing data. Synology puts the difference plainly: an external drive "does not allow for multiuser access."

What an external hard drive does well

An external hard drive connects over USB to one computer at a time — QNAP notes a USB drive is typically attached to one device. There's nothing to configure: plug it in and it shows up. It uses no power when unplugged, usually costs far less than a NAS setup, and travels easily.

Speed depends on the USB standard. Many desktop external drives use USB 3.2 Gen 1 (per WD's Elements Desktop data sheet), which is plenty for backups and file storage:

• USB 3.2 Gen 1: 5 Gbps
• USB 3.2 Gen 2: 10 Gbps
• USB 3.2 Gen 2x2: 20 Gbps

What a NAS adds

A NAS sits on your network instead of your desk, so every device in the house — laptops, phones, TVs, a work PC — can reach the same files at the same time. There's no question of which computer the drive is plugged into.

It also runs services continuously: scheduled backups from several machines, media servers, and remote access from outside the house. With two or more drives in RAID, one drive failing doesn't take your data with it. A single external drive can't do any of that.

Cost and power

A NAS costs the enclosure plus the drives — the enclosure has no storage of its own — and those drives should be CMR NAS-class drives. An external hard drive is one purchase, ready to use.

A NAS also runs around the clock. By Synology's specs, a 2-bay DS224+ draws about 14.7 W while accessing drives and 4.4 W with drives hibernating; a 4-bay DS923+ about 35.5 W accessing and 11.5 W hibernating. A single 3.5-inch desktop hard drive is rated roughly 5 to 9 W operating, and nothing while it's unplugged.

Neither is a backup on its own

This is the part people get wrong. A NAS with RAID protects against a drive failure, not against deletion, theft, or the whole unit failing — Synology's own FAQ says RAID "does not replace having separate backups." An external drive holding your only copy isn't a backup either.

The standard fix is the 3-2-1 rule, as described by CISA and Backblaze:

• Keep 3 copies of your data: the original plus 2 backups.
• Store them on 2 different types of media.
• Keep 1 copy offsite.

Use both: an external drive as a NAS backup target

If you run a NAS, an external hard drive is a natural companion. Synology's Hyper Backup can back up a NAS to a USB drive, and models such as the DS923+ have USB 3.2 Gen 1 ports for it. That gives you a second copy on separate media that you can unplug and store away from the NAS; add an offsite copy — cloud storage or a drive kept elsewhere — to complete 3-2-1.

Which should you buy?

• An external hard drive, if one computer needs extra space or backups and you want the cheapest, simplest option.
• A NAS, if several devices need shared access, you want always-on services like scheduled backups or a media server, or you want RAID protection against a drive failure.
• Both, if you have a NAS and want a real backup plan — the external drive becomes a second copy.
• Neither alone as your only backup: follow 3-2-1 whatever you buy.