Best External Hard Drives for NAS Backups

Quick Summary (TL;DR):
For NAS backup, prioritise capacity, warranty, simple USB compatibility and the ability to disconnect/rotate the drive—not headline interface speed. Our best all-round desktop backup choice is WD My Book: current models run from 4TB to 26TB, use USB 3.2 Gen 1 and carry a 3-year limited warranty. The simpler WD Elements Desktop is excellent when you want a basic plug-in backup target; current models also reach 26TB and carry a 2-year warranty. Seagate Expansion Desktop currently reaches 30TB in the UK range and carries a 2-year warranty, making it attractive when one external drive must hold a very large NAS backup. Seagate One Touch Hub currently reaches 20TB and adds front USB ports plus Seagate Toolkit support. For smaller off-site rotations, WD My Passport USB-C reaches 6TB, is bus-powered and carries a 3-year warranty. Whichever model you choose, buy enough capacity for the actual backed-up dataset plus versioning/headroom, use at least two rotating drives if the data matters, and keep one disconnected when not backing up. An external USB HDD permanently attached to the NAS is convenient, but it is not truly offline protection.

Best External Hard Drives for NAS Backups: Shortlist

External drive	Current max capacity	Warranty	Best use
WD My Book	26TB	3 years	Best all-round desktop NAS backup
WD Elements Desktop	26TB	2 years	Simple/value high-capacity rotation
Seagate Expansion Desktop	30TB	2 years (UK)	Largest single-drive backup option
Seagate One Touch Hub	20TB	2 years (UK)	Backup drive + extra USB hub
WD My Passport USB-C	6TB	3 years	Portable/off-site rotation

The Best NAS Backup Drive Is Not the Fastest External Drive

NAS backups are normally capacity-first workloads. A single mechanical hard drive will not come close to saturating a 5Gb/s USB 3.x connection during ordinary sequential backup use.

Backup speed is more likely to be limited by the HDD itself, the NAS CPU, encryption, file count or the source storage pool. That means USB 3.0 versus USB 3.2 Gen 1 branding should not decide the purchase.

Size the Backup from Used Data, Not Raw RAID Capacity

Do not look at a 48TB RAID and assume you need a 48TB external drive. Look at the data you actually intend to protect.

NAS raw capacity:          48TB
actual used data:          17TB
selected backup data:      14TB
version history/headroom:  required

→ a 16TB target may be too tight
→ 20TB+ gives safer growth room

A simple mirror/copy needs relatively little headroom. A versioned backup can need much more because old versions and deleted files are retained.

Best Overall: WD My Book

WD My Book is our easiest general recommendation for a single-drive desktop NAS backup.

• Current capacities from 4TB to 26TB.
• USB 3.2 Gen 1 / USB 3.0 compatibility.
• External AC power supply.
• 3-year limited warranty.
• WD device-management/backup software for supported computers.

For direct NAS attachment, the bundled PC software is mostly irrelevant because the NAS runs the backup job. The real advantages are broad capacity choice and the longer warranty versus many entry-level desktop externals.

Why 22TB–26TB My Book Models Are Useful

A large single external drive can back up a substantial four-bay NAS without needing a multi-drive USB enclosure.

• 22TB: WDBBGB0220HBK series.
• 24TB: WDBBGB0240HBK series.
• 26TB: WDBBGB0260HBK series.

Keeping the backup on one removable drive also makes rotation and off-site storage simpler.

Best Simple High-Capacity Option: WD Elements Desktop

WD Elements Desktop is the simpler alternative.

• Current 4TB–26TB range.
• USB 3.2 Gen 1.
• External AC power.
• 2-year limited warranty in the current European range.
• Simple plug-and-play positioning.

For a NAS-controlled backup job, simplicity can be an advantage. Synology Hyper Backup, QNAP HBS 3, UGREEN backup tools or rsync handle the data copy; the external drive only needs to be a reliable storage target.

My Book vs Elements Desktop

Feature	WD My Book	WD Elements Desktop
Maximum current capacity	26TB	26TB
Interface	USB 3.2 Gen 1	USB 3.2 Gen 1
Warranty	3 years	2 years
Software/features	More	Minimal/simple
Best reason to buy	Warranty/features	Simplicity/value

If prices are close, we prefer My Book for the extra year of warranty. If Elements is materially cheaper, it is an excellent NAS backup target.

Largest Single-Drive Option: Seagate Expansion Desktop

Seagate’s current UK Expansion Desktop range reaches 30TB.

• Current UK models include 8TB, 16TB, 20TB, 24TB and 30TB.
• USB 3.x interface.
• 2-year limited warranty in the current UK range.
• External power supply.

For a NAS containing 20TB+ of selected backup data, a 30TB single external drive is useful because it can avoid building a second multi-drive array purely for local backup.

Best with Extra USB Ports: Seagate One Touch Hub

Seagate One Touch Hub makes more sense when the drive also sits beside a PC/server and you want additional USB connectivity.

• Current UK capacities up to 20TB.
• 2-year limited warranty.
• External power.
• USB hub functionality.
• Seagate Toolkit support for computer-based workflows.

For a drive connected only to a NAS USB port, the hub adds little value. The simpler Expansion line is usually enough.

Best Portable Rotation: WD My Passport USB-C

Portable HDDs are useful when the backup copy must leave the house regularly.

• 2TB, 4TB, 5TB and 6TB capacities.
• USB 3.2 Gen 1 / USB-C connectivity support.
• Bus-powered.
• 3-year limited warranty.

A 6TB portable drive is ideal for critical subsets such as documents, photos and configuration backups. It is not large enough for many complete NAS datasets.

Do You Need CMR for an External Backup Drive?

Not necessarily. Backup is one of the workloads where SMR can be acceptable because many jobs consist of large sequential writes followed by mostly reads.

The bigger problem is transparency: external-drive manufacturers generally specify the external product SKU, capacity, interface and warranty, but do not guarantee that every unit or revision contains the same bare internal HDD model.

If your requirement is “I must receive this exact CMR model”, buy a bare NAS/enterprise HDD and put it in a USB enclosure instead.

Shucking Is the Wrong Direction for a Backup Drive

“Shucking” means opening an external enclosure and using the internal HDD elsewhere. It can look attractive when an external drive is cheaper than a bare HDD.

For NAS backup, we generally prefer leaving the product intact:

• The exact internal drive may not be guaranteed.
• Warranty handling becomes more complicated.
• You lose the convenient removable backup unit.
• The enclosure/electronics may have model-specific quirks.

If you want full control over the internal drive, Article 54 covers the better approach: Best USB Drive Enclosures for Rotating Offline NAS Backups.

One External Drive Is Not Enough for Important Data

A better design is two rotating drives:

Week A
NAS → Backup Drive A
safe eject
store offline/off-site

Week B
NAS → Backup Drive B
safe eject
store offline/off-site

repeat

If one drive fails or one backup generation is corrupted, the other rotation still exists.

Always-Connected USB Backup Is Not Offline Backup

A permanently attached external HDD is convenient for scheduled jobs and is still useful protection against failure of the main storage pool.

But it remains exposed to some of the same events as the NAS:

• Ransomware or malicious deletion with access to the target.
• Electrical damage.
• Fire/theft at the same location.
• Administrative mistakes.

For stronger protection, physically disconnect at least one backup copy when the job finishes.

Use Safe Eject before Disconnecting

Never pull the USB cable while the NAS is writing. Use the NAS’s eject/unmount function and wait until the external volume is safely detached.

Desktop 3.5-inch drives also need their own power adapter. Label each drive and its matching PSU so a restore is not delayed by a missing power brick.

Filesystem Choice Should Consider Disaster Recovery

A NAS can format USB backup drives with different filesystems depending on the platform.

• A NAS-native filesystem may give the best backup-tool integration.
• A portable filesystem may be easier to read directly on Windows/macOS/Linux if the NAS itself is dead.

Choose deliberately and test the restore path before you need it.

Encrypt Drives That Leave the House

An off-site drive can be lost or stolen. Use backup encryption for personal or confidential data and store the recovery key independently from both the NAS and the external disk.

NAS-managed encryption is often easier to document than relying on proprietary desktop-drive software, especially when the recovery process may happen years later.

A Backup You Cannot Restore Is Not a Backup

After the first backup:

• Restore several files somewhere else.
• Open photos/videos/documents.
• Test encrypted-backup credentials.
• Verify version history.
• Document the recovery steps.

Repeat restore tests periodically.

How Much Capacity Should You Buy?

Backed-up dataset today	Practical external-drive direction	Reason
Up to ~3TB	4–6TB	Room for growth/versioning
~4–6TB	8–10TB	Comfortable headroom
~8–10TB	12–16TB	Versioning/growth
~12–16TB	18–22TB	Avoid near-full backup target
~18–22TB	24–30TB	Large single-drive local backup
Above ~25TB	Multi-drive enclosure / second NAS	Single-drive ceiling becomes restrictive

These are planning ranges, not hard rules. A fast-changing or heavily versioned dataset may require much more space.

When One 30TB Drive Is Better Than USB RAID

If the complete backup fits comfortably on one disk, a single-drive target has important advantages:

• Simple recovery.
• No RAID-controller dependence.
• Easy physical rotation.
• Easy off-site storage.
• Low setup complexity.

A multi-drive DAS becomes useful when the dataset exceeds one practical drive or when capacity requirements demand several disks.

A Practical Buying Matrix

Scenario	Best direction	Why
General 10–25TB NAS backup	WD My Book	3-year warranty + broad capacity range
Simple/value rotation	WD Elements Desktop	Minimal features, up to 26TB
Need maximum single-drive capacity	Seagate Expansion Desktop	Current UK range reaches 30TB
Drive also sits beside PC/server	Seagate One Touch Hub	Extra USB ports + Toolkit
Small off-site critical-data copy	WD My Passport USB-C	Bus-powered, portable, up to 6TB
Need guaranteed exact HDD/CMR model	Bare HDD + USB enclosure	You choose the internal drive
Dataset exceeds one large HDD	Multi-drive enclosure / second NAS	Single-drive ceiling reached

Best External Hard Drives for NAS Backups: The Bottom Line

WD My Book is our best all-round choice. Its 4TB–26TB range and 3-year warranty make it a strong fit for rotating desktop NAS backups.

WD Elements Desktop is the simple/value alternative. It reaches the same 26TB ceiling but gives up some features and one year of warranty.

Seagate Expansion Desktop is the capacity winner. The current UK range reaches 30TB, which can keep a very large home NAS backup on one removable disk.

Seagate One Touch Hub makes sense when you need its hub functionality. For a drive connected only to a NAS, the simpler Expansion line is usually enough.

WD My Passport is the best fit for smaller off-site rotations. Up to 6TB is modest by NAS standards, but bus power and portability make it easy to remove from the building.

Most importantly, buy the external drive as part of a backup system rather than as an isolated product. Keep enough free capacity for retention, safely eject it, disconnect at least one copy, rotate media, encrypt off-site copies and test restores. Two ordinary external HDDs used properly are more valuable than one premium drive that never leaves the NAS.

Continue the NAS Backup Series

• Best USB Drive Enclosures for Rotating Offline NAS Backups
• A 3-2-1 NAS Backup Plan: USB Drive, Second NAS and Cloud

Datasheets & External Resources

• Western Digital My Book – Current capacities and warranty
• Western Digital Elements Desktop – Current capacities and warranty
• Western Digital My Passport USB-C – Current capacities and warranty
• Seagate Expansion Desktop – Current UK capacities and warranty
• Seagate One Touch Hub – Current UK capacities and warranty