Buying a Two-Drive NAS? RAID 1 Is Not a Separate Backup Copy

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Short answer: No. The second drive in a RAID 1 pair is redundancy against a failed disk, not a separate backup copy. QNAP’s own explanation says plainly that "RAID IS NOT a backup" and that it "mainly guards against hardware failures". Deletion, corruption, viruses, theft and disasters can still take the data. So when you budget for the NAS and its two drives, budget for a separate recovery copy too.

Scope: this guide uses QNAP’s general RAID explanation and the RAID 1 row of the QTS 5.2 user guide as its example, checked on October 16, 2026 (KST). We did not buy, install, fail or restore a NAS. Other models, operating systems and RAID settings can behave differently.

Two drives are not two independent copies

In QNAP’s QTS 5.2 RAID table, RAID 1 uses 2 disks, has a disk failure tolerance of 1, and its capacity is "Half of the total combined disk capacity". QNAP describes the layout in one line: "An identical copy of data is stored on each disk." (QTS 5.2 RAID types)

That identical copy is the strength and the limit. Both disks carry the same current data, which is why one disk can fail without losing it. A second disk with the same current data is not an older version to go back to, and QNAP separately lists accidental deletion and file corruption among the risks RAID alone does not cover (RAID = Backup?).

Two more lines from the guide matter at checkout:

  • The capacity figure is nominal. If disks with different capacities are combined in one RAID group with disk failure tolerance, QNAP says "all disks function according to the capacity of the smallest disk." The free space you actually see after setup is not something this guide can tell you.
  • Matched disks are recommended. For best performance and space efficiency, QNAP says to use disks of the same brand, disk type and capacity when creating a RAID group.

What RAID 1 covers, and what it doesn’t

One drive fails. This is what RAID 1 is for: the QTS 5.2 table lists a disk failure tolerance of 1.

A file is deleted or corrupted. Not covered by RAID alone. QNAP’s list includes accidental deletion and file corruption from memory errors or power failure.

Viruses. QNAP’s list includes them.

The NAS itself is lost. QNAP’s list includes theft of your system and disasters such as a fire or water poured onto the NAS. A second disk inside the same box is exposed to the same event.

QNAP’s rule of thumb for a sound backup strategy: "make at least two copies of your data, and keep at least one of which is stored offsite."

A blank worksheet to fill in before checkout

We don’t know your data, budget or setup, so nothing below is pre-filled, totaled or promised.

  1. Which data would actually hurt to lose? ______
  2. Where does the original (live) copy sit? ______
  3. Where will the separate copy go: another device, a service, or another NAS? ______
  4. How far back do you need to recover a file (retained history)? ______
  5. Who and what can reach that separate copy (access, isolation)? ______
  6. Does one copy need to be offsite? ______
  7. How will you confirm a restore works, using the vendor’s own documentation? ______
  8. Upfront cost and ongoing cost of the separate copy, quoted separately: ______

If item 3 is still blank, the NAS plan is a storage plan, not a backup plan yet.

Planning the same purchase from other angles: checking a UPS before you buy a NAS and how Backblaze shows older versions of files from an external drive.

Replacing a failed drive later? Back up first

QNAP’s FAQ How do I replace a faulty disk in a RAID group? (last modified 2026-01-08; applicable to QTS 4.5 and later and QuTS hero h4.5 and later) includes an important note: "Before you replace a faulty disk, back up all data on the NAS." It adds that if your NAS does not support hot-swapping disks, you power it off before removing a faulty disk, and that you check hot-swap support for your exact model in its hardware specs. Follow QNAP’s steps for your RAID type there.

FAQ

Is RAID 0 a better use of two drives? Not for protection. In the same QTS 5.2 table, RAID 0 "Provides no disk failure protection" and "must be paired with a data backup plan." It trades protection for speed and the total capacity of both disks.

Can a NAS be a backup at all? Yes, when it holds a separate copy of an original that lives somewhere else. QNAP’s own example is to "store the original copy/data on your computer, and also keep a copy on your NAS with RAID." The point is where the copies are, not the box.

What should I check before replacing a disk? Back up all data on the NAS first, then check whether your model supports hot-swapping disks before you remove anything (QNAP FAQ above).

Sources

Checked on October 16, 2026 (KST):