Best 20TB NAS Drives UK 2026: Price per TB Ranked
20TB NAS-rated CMR drives by price per TB
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The best-value 20TB NAS drive is the Seagate IronWolf Pro ST20000NE000 (ASIN B0BRYNHNPB) at around £610.77, working out to £30.54/TB at last check on 24 July 2026. It's a proper NAS-rated CMR drive with a 256MB cache and 7,200rpm performance, and at this price it undercuts every other 20TB CMR option on the list by a wide margin. Unless you specifically need enterprise firmware or extended MTBF ratings, this is where your money should go. Everything above it on price is either a duplicate listing at a worse rate or a step up into enterprise territory you probably don't need at home.
Best 20TB NAS drives
All ten drives here are CMR (conventional magnetic recording), which is the only sensible choice at 20TB for RAID. Prices and £/TB are indicative as checked on 24 July 2026 and will drift, so treat the ranking as the durable bit.
Which 20TB drive should you buy
Choose the IronWolf Pro ST20000NE000 if
- You want the lowest £/TB on a genuine NAS-rated CMR drive
- You're filling a 4 to 8-bay NAS and buying multiple drives, where the saving multiplies
- You want IronWolf Health Management and Seagate's Rescue data recovery service included
- You don't need enterprise-class vibration tolerance beyond typical 8-bay desktop NAS use
Choose the WD Ultrastar HC560 if
- You're running a rack-mounted NAS or a build with 12+ bays and want enterprise vibration tolerance
- You need the higher workload rating for near-constant read/write, not just backup and media serving
- Budget is secondary to long-term duty-cycle confidence for business-critical storage
- You're building a large pool where drive failure and rebuild risk needs the extra margin enterprise drives are designed for
Who actually needs 20TB, and CMR vs SMR at this capacity
20TB drives make sense once you're building a pool that needs to comfortably exceed 40 or 60TB usable, typically in a 4-bay or larger NAS running RAID 5, RAID 6, or Synology's SHR. If you only need 10 to 20TB total, two or three smaller drives (or even a pair of 12TB drives) will usually cost less overall and rebuild faster if one fails. Where 20TB earns its keep is in media libraries, business backup targets, or surveillance archives where you want maximum capacity per bay without adding more drives, more power draw, and more vibration into the chassis.
At 20TB, the CMR versus SMR question isn't really a question, it's a hard rule: buy CMR only. Shingled Magnetic Recording (SMR) drives write data in overlapping tracks to boost capacity cheaply, but this makes random writes and RAID rebuilds painfully slow, and in some cases rebuilds simply time out and fail, taking your array with them. Every drive on this list is CMR, which is exactly why they're the only sensible options at this capacity. The manufacturers have largely stopped selling SMR at 20TB in NAS-branded lines, but always check the datasheet before buying from a listing that isn't explicitly confirmed CMR, because retailers do occasionally mix stock.
The rebuild risk you need to plan for at 20TB
A 20TB drive rebuild in RAID 5 or RAID 6 can take the best part of a day, sometimes longer, and during that window your array has reduced or zero redundancy. This is precisely why CMR matters so much here: an SMR drive under sustained rebuild write load can slow to a crawl or drop out, and at 20TB per drive that's a lot of data resting on a single point of failure for an extended period. If you're building a large pool, favour RAID 6 or SHR-2 over RAID 5 once you're using 20TB drives, and keep a cold spare on hand. Don't treat any single 20TB drive, however well-rated, as your only copy of anything irreplaceable.
20TB NAS drives, by price per TB
Prices are indicative — last checked 8 September 2026, from Amazon.co.uk. They are not live; check the current price on Amazon before buying. Best £/TB is the lowest at last check.
Frequently asked questions
Is the cheapest 20TB drive on this list actually reliable enough for a NAS?
Yes. The Seagate IronWolf Pro ST20000NE000 at around £610.77 is a NAS-rated CMR drive with the same core reliability features (vibration sensors, NAS firmware, 7,200rpm CMR platters) as pricier options. The lower price reflects the specific listing and retailer at the time of checking, not a lesser drive.
Should I buy WD Red Pro or Seagate IronWolf Pro for a 20TB build?
Both are solid NAS-rated CMR drives with comparable warranties and workload ratings. At last check, IronWolf Pro options were consistently cheaper per terabyte, which makes them the more sensible default unless you have a specific reason (existing WD-only pool, preferred RMA experience) to pay more for Red Pro.
What's the difference between the IronWolf Pro and the Exos X20?
Exos is Seagate's enterprise line, built for data centre workloads with higher rated duty cycles and typically deployed in large rack arrays. At around £1,484.98 (£73.51/TB) for the X20 in this list, it's priced well above home and small business NAS use cases, and the IronWolf Pro line covers the same CMR reliability at a much lower cost for typical NAS duty cycles.
Can I mix 20TB drives from different brands in the same NAS?
Technically yes, most NAS systems don't require identical drives, but for RAID arrays it's best practice to match drives as closely as possible in capacity and ideally brand and batch, to keep rebuild behaviour predictable and avoid subtle firmware timing mismatches.
How many bays do I need to make 20TB drives worthwhile?
Realistically four bays or more. In a two-bay NAS, 20TB drives in RAID 1 give you 20TB usable at a high cost per bay; you'd often do better with two 12TB or 14TB drives. The value case for 20TB strengthens as bay count rises, since fixed costs (chassis, controller) are spread across more capacity.