Should you replace the hard drives in your NAS?

Every few months a new reliability study does the rounds and NAS owners start eyeing their drive bays nervously. In September 2026 XDA Developers' Rich Edmonds re-evaluated every drive in his NAS after a large peer-reviewed study reported that, controlling for age and temperature, some manufacturers' drives failed roughly twice as often as others. His conclusion was not to panic-buy. Ours is the same — but it is worth doing the review properly.

Population statistics are not a verdict on your drive

A study of hundreds of thousands of drives tells you which groups fail more often. It says very little about the specific disk spinning in bay three. As our Seagate vs WD analysis shows, the model matters far more than the badge: two drives from the same brand can differ several-fold in failure rate. A healthy four-year-old drive with clean SMART data is not suddenly a liability because its maker scored badly in a table.

The re-evaluation checklist

Work through these for each drive. Anything that fails the first two is a replace-now; the rest shape how you plan the next refresh.

SMART health. Reallocated, pending and uncorrectable sectors that are non-zero — and especially rising — are the clearest warning you will get. Our five SMART numbers that matter guide explains exactly what to look for. A drive showing these belongs in the bin, not the array.
Errors in the NAS log. Read/write errors, a drive dropping out of the array or scrubs finding checksum errors mean act now, regardless of what SMART says.
Age and power-on hours. Failure rates climb once drives pass roughly five years of 24/7 use (about 44,000 power-on hours). Drives in the same array were usually bought together, so they age together — see how long hard drives last.
Temperature. Heat is the cheapest thing to fix. The study XDA covered linked each extra degree Celsius to a small but compounding rise in failures. Check drive temperatures in your NAS dashboard: mid-30s °C is comfortable, sustained high-40s is not. A faster fan profile or better airflow is free reliability.
SMR drives. Shingled (SMR) drives can make RAID rebuilds painfully slow, which lengthens the window where a second failure loses data. If your array contains any, plan to swap them for CMR — see SMR vs CMR.
Brand and batch mix. If every drive is the same model from the same batch, a shared defect can take out several at once. You do not need to replace working drives to fix this — just buy replacements from a different batch or brand as drives retire.

When consolidating to bigger drives pays

Often the best reason to replace NAS drives is not reliability at all — it is that fewer, larger drives are cheaper to run and simpler to manage. Fewer spindles mean less heat, less vibration, lower power draw and fewer things that can fail.

The maths depends on today's prices. At the time of writing (September 2026), new NAS and enterprise drives on Amazon UK sit at roughly £30–£40 per TB across 4TB to 24TB, with the mid-size 12TB and 16TB drives usually at the cheaper end. Prices moved sharply up through 2025–26 as AI data-centre demand soaked up supply, so check the live tables rather than older rules of thumb.

A worked example: an older six-bay NAS full of 4TB drives gives about 20TB usable in single-parity RAID. Three 16TB drives in the same layout give about 32TB usable — 60% more space from half the drives, with three bays left free to grow into later. Whether it is worth doing now comes down to the checklist above: if the 4TB drives are healthy and cool, run them until space or SMART forces your hand, and buy the bigger drives when prices dip.

How to replace drives safely

Back up first. RAID is not a backup. A rebuild stresses every remaining drive, and that is exactly when an ageing sibling tends to fail.
One drive at a time. Replace, let the array fully rebuild and scrub, then move to the next.
Test new drives before trusting them. A full surface scan or extended SMART test catches early-life failures before they hold your data.
Consider warehouse and renewed units carefully. They can save a lot, but know what you are buying — see drive conditions explained.

See NAS drives ranked by £/TB Drive reliability data

Frequently asked questions

Should I replace my NAS drives because a study says my brand is less reliable?

Not on that basis alone. Reliability studies describe large populations, not your individual drive. Replace drives that show SMART warnings, NAS errors or are well past five years of 24/7 use; otherwise diversify brands and batches as drives naturally retire.

How old is too old for a NAS hard drive?

There is no hard cut-off, but failure rates rise noticeably after about five years of continuous running (roughly 44,000 power-on hours). Watch SMART data closely from that point and plan replacements before several same-age drives start failing together.

Does drive temperature really affect NAS reliability?

Yes. Large studies consistently link higher operating temperatures with higher failure rates. Keeping drives in the mid-30s °C with good airflow or a more aggressive fan profile is the cheapest reliability improvement you can make.

Is it worth replacing several small NAS drives with fewer large ones?

Often, yes — fewer drives mean less heat, power and vibration and fewer failure points. Compare the price per TB of larger drives on our live tables; when it is similar or lower than your current drives, consolidation usually pays over the life of the NAS.