Below, a dated US price example compares approximately 4 TB of destination capacity, a separate backup device and three years of electricity. It is a calculated scenario, not a hardware benchmark or a claim to identify the cheapest products. The distinction that matters is whether you need a storage device or a small server you will maintain.
The short answer
Buy for the job you repeat
Sharing, availability and maintenance determine whether the extra cost helps.
- One main computerA USB drive suits one main computer and a person willing to connect it for backup. Software can schedule those backups while the device is available.
- Several connected devicesA NAS can serve several devices without keeping one desktop computer switched on, but adds administration and network dependencies.
- Another recovery routeBudget independent backup in both cases. Two mirrored disks inside one NAS do not cover every way files can be lost.
Decide who needs access and when
A direct-attached USB drive is physically connected to a host. That makes the arrangement easy to understand: connect it, select the folders or configure backup software, verify the result and safely disconnect it when appropriate. A desktop model may need its own power adapter; a portable model may take power through USB.
A NAS connects to the network and provides services to authorized users and devices. It can be a common destination for family computers or a shared collection that does not depend on whoever last carried a USB drive away. You still need compatible applications, user permissions and a working network. A device merely supporting a service does not mean that the service has been configured correctly.
For one laptop used mostly away from home, a USB drive plus an offsite backup can be the less demanding arrangement. For several computers that need unattended backups, a NAS that remains available can remove the routine of moving a cable between machines. If the desired job is only a quarterly photo export, that convenience may not justify owning another continuously maintained system.
A USB drive can also be shared through a computer or a compatible router. That can be sufficient for a modest need, but its availability, permissions, software and performance then depend on that host. Compare that actual arrangement with the NAS rather than assuming that USB storage can never be shared.
Separate capacity from resilience
Diskless NAS prices omit the drives. In a two-disk RAID 1 arrangement, data is mirrored and usable array capacity is limited by the smaller member. QNAP explains that capacity rule. Two 4 TB disks therefore provide roughly 4 TB before filesystem and system overhead, rather than 8 TB for your files.
That mirror can keep data available after one member fails. It does not independently preserve yesterday's version of a file, protect against theft of the whole box or guarantee recovery after a mistaken deletion. Snapshots and versioned backups add different capabilities; a snapshot kept on the same appliance still depends on that appliance surviving.
Leave capacity for growth, retained versions and any reserved snapshot space. A nominal 4 TB backup disk is not automatically adequate for a nearly full 4 TB source plus months of versions. Check the amount of changed data and the backup software's actual retention behavior.
If you are still choosing the physical storage medium, our SSD versus HDD comparison addresses that separate question. The NAS decision adds network access, user management and maintenance on top of the medium.
A three-year example with the backup included
This scenario starts with a 2 TB collection whose originals remain on an already-owned computer. Both options add around 4 TB of destination capacity and a separate 4 TB external drive for an additional backup kept elsewhere between jobs. That leaves some headroom; whether it is enough for version history depends on changes to the collection.
Prices below were checked on October 31, 2026, in US dollars, before sales tax. These are specific B&H listings, not market-wide minimums. Shipping, optional installation, replacement drives, paid software and cloud subscriptions are excluded. They must be added if your plan needs them.
NAS enclosure — $239. The QNAP TS-233-US listing is for the two-bay enclosure. Its storage disks are additional purchases.
Two NAS disks — $478. Two 4 TB Seagate IronWolf ST4000VN006 drives at $239 each bring that hardware subtotal to $717. RAID 1 supplies roughly 4 TB of array capacity before overhead. Verify the current NAS compatibility list for the exact disk model and firmware before purchasing.
External drive — $189.99 each. The 4 TB Seagate Expansion STNN4000400 was listed at $189.99. This is the current model in the calculation, not the older STKM4000400. The USB option uses two units, totaling $379.98. The NAS option adds one unit to its $717 subtotal, totaling $906.99.
In both cases, the additional external drive must actually receive a separate backup and be stored appropriately. Moving all originals off the computer would change the copy count and require a revised protection plan. Buying the listed devices alone does not implement 3-2-1.
For electricity, use an explicit scenario rather than the power adapter's maximum rating. QNAP lists 10.81 W typical operating consumption with drives populated. Applying that figure continuously for three 365-day years at an assumed $0.20 per kWh gives $56.82. It is a model based on a manufacturer's stated typical figure, not a measurement of the two drives listed above in this household.
The calculation is watts divided by 1,000, multiplied by hours and the electricity rate. For the USB working destination, assume 4 W for eight hours per day: $7.01 over three years. For the additional backup drive in either option, assume 4 W for two hours weekly over 156 weeks: about $0.25. These USB power figures and connection times are modeling assumptions, not manufacturer specifications.
Modeled three-year total — NAS $964.06; USB $387.24. The difference is $576.82, or about $16.02 per month over 36 months. Totals are rounded after calculation. They exclude the already-owned computer and router, their energy use, and the exclusions above. If you must keep a computer running only to share the USB drive, add that incremental electricity and any other costs to the USB side.
Do not generalize this difference into “every NAS costs $577 more.” Different disks, capacities, discounts, electricity rates and operating hours change the result. In this example, hardware accounts for most of the premium. Doubling the modeled electricity rate adds about $56.82 to the NAS's main-device energy cost, while the enclosure-and-drive purchase remains the larger decision.
Check the slowest connection in the actual job
The TS-233 specification lists one Gigabit Ethernet port. One gigabit per second is 125 megabytes per second before protocol overhead. That conversion is a ceiling on the link's raw rate, not a measured file-copy speed. Other clients and workloads can share that connection.
Wi-Fi quality, the client computer, drive behavior and small-file overhead can all affect a real transfer. Similarly, a USB interface's advertised rate is not the sustained write speed of the hard disk inside its enclosure. Compare the whole route for the task: opening a large video project locally, copying a photo archive or backing up several computers concurrently.
A portable SSD may be more useful for active editing than either of the HDD arrangements priced here. A faster NAS network may help a different workflow, but only if the client, switch and cabling support it. Those are different configurations with additional costs; this example does not benchmark them.
Allow for the work that follows the purchase
A NAS needs an owner for updates, accounts, disk warnings and backup failures. Use individual permissions instead of giving every device unrestricted access. Check the manufacturer's supported software lifecycle before choosing an older model just because its purchase price is low.
Remote access is a separate configuration decision. QNAP's security guidance includes current software, account protections and disabling UPnP port forwarding. Do not expose a management interface to the internet merely to make setup convenient. Use a properly configured access method and maintain it.
USB storage requires less server administration, but still needs discipline: the drive must be present when the backup runs, the job must include the intended folders and the result must be checked. Windows File History supports external and network destinations, so scheduled file versions are not exclusive to a NAS. Our Windows Backup guide explains a different, account-based mechanism and its limits.
Choose the NAS when recurring shared access or unattended work is valuable enough to justify the full cost and someone will maintain it. Choose USB when one computer, straightforward capacity and a repeatable connection routine meet the need. In either case, finish with a tested recovery plan and a copy that does not depend on the main storage surviving.
