Best 20 TB Hard Drives for NAS

For a NAS that supports the exact model, buy the Seagate IronWolf Pro ST20000NT001 first: this 20 TB CMR SATA drive combines a 550 TB/year workload rating with a five-year limited warranty and three years of Rescue coverage where available. The WD Red Pro WD202KFGX is our alternative, with the same published workload and warranty duration; choose between them using your enclosure's exact compatibility entry and the seller's warranty route. Below is a verified enclosure-and-backup example, plus the capacity and replacement checks to make before ordering a whole set.

Quick picks: compare the exact 20 TB drives

Both picks are 3.5-inch CMR SATA drives running at 7,200 RPM. The speed figures below are manufacturer maximum sequential rates, not measured file-copy speeds through a NAS.

Compare specifications and all conditions

Best overall

Exact model

Seagate IronWolf Pro ST20000NT001

Maker's maximum sequential rate

285 MB/s

Workload rating per drive

550 TB/year

All specifications

Limited warranty

Five years

Included recovery term

Three years of Rescue, subject to country availability

Best alternative

Exact model

WD Red Pro WD202KFGX

Maker's maximum sequential rate

285 MB/s

Workload rating per drive

550 TB/year

All specifications

Limited warranty

Five years

Included recovery term

Not specified in the cited Red Pro sheet

Full comparison table ↔

Swipe to compare. Row labels stay visible.

Pick	Exact model	Maker's maximum sequential rate	Workload rating per drive	Limited warranty	Included recovery term
Best overall	Seagate IronWolf Pro ST20000NT001	285 MB/s	550 TB/year	Five years	Three years of Rescue, subject to country availability
Best alternative	WD Red Pro WD202KFGX	285 MB/s	550 TB/year	Five years	Not specified in the cited Red Pro sheet

Pick	Exact model	Maker's maximum sequential rate	Workload rating per drive	Limited warranty	Included recovery term
Best overall	Seagate IronWolf Pro ST20000NT001	285 MB/s	550 TB/year	Five years	Three years of Rescue, subject to country availability
Best alternative	WD Red Pro WD202KFGX	285 MB/s	550 TB/year	Five years	Not specified in the cited Red Pro sheet

Sources: Seagate generation table and WD exact-model sheet. Warranty duration assumes an eligible purchase; it does not verify a seller's offer.

Best overall: Seagate IronWolf Pro ST20000NT001

Choose the NT001 when its exact compatibility entry matches your NAS and you value the included recovery service. Seagate specifies CMR, rotational-vibration sensors and a 550 TB/year workload rating for this model. Its five-year limited warranty and three-year Rescue term are separate commitments; Seagate says Rescue is unavailable in some countries. Confirm eligibility before paying for a listing on that basis.

Do not merge it with ST20000NE000. Seagate's table gives that other 20 TB model a 300 TB/year workload rating and support for up to 24 bays, versus unlimited bays for NT001. A drive-family bay rating does not certify a particular enclosure.

There is also an official specification conflict: DS1914.21 lists 256 MB cache for ST20000NT001; DS2129.1 lists 512 MB in its 20 TB NT001 column. We flag both and do not rank it by cache size. Ask Seagate to confirm the shipped revision if that distinction matters to your purchase.

Check the official IronWolf Pro specifications.

Best alternative: WD Red Pro WD202KFGX

Choose WD202KFGX when it fits your enclosure's list or purchasing channel better. WD specifies 20 TB, CMR, 512 MB cache, 7,200 RPM, 550 TB/year and a five-year limited warranty.

The suffix matters here too: WD's sheet lists WD201KFGX separately, with a maximum internal transfer rate of 268 MB/s, versus 285 MB/s for WD202KFGX. Do not accept that suffix as an automatic substitute on either specifications or enclosure support. The two models both have 20 TB capacity and 512 MB cache in that sheet.

WD's warranty policy requires an authorized distributor or reseller for its HDD limited warranty; system-integrated drives go through the system maker. Keep the invoice and verify the serial number's regional eligibility.

Check the exact WD202KFGX model and specifications.

How we choose

This is manufacturer-document research, without physical drive testing. We compare exact model columns, recording technology, workload, warranty and recovery terms, then cross-check the same disks against both the primary enclosure and backup enclosure. The selection uses official drive sheets, QNAP's current compatibility feeds and versioned QTS instructions, checked November 2, 2026. We make no measured reliability, noise or rebuild-time ranking. See how we choose; our broader NAS hard-drive guide covers the general buying decision.

Buying guide: prove enclosure support first

Here is a concrete match: QNAP's current TS-464 list and TR-004 list both contain these entries:

These are documented combinations, not a certification of every suffix, future firmware or other NAS. Before checkout, look up your enclosure model, drive suffix, firmware, OS and pool/volume limits. An existing 8 TB entry does not establish 20 TB support. Buy the documented SATA version for this example; a same-capacity SAS offer needs its own explicit support confirmation.

• Yes: Match the enclosure and full drive label against its current compatibility list
• Yes: Check the backup enclosure independently
• Partly: A different suffix or firmware needs confirmation
• No: Capacity and brand alone do not establish compatibility

If your present enclosure already passes those checks, keep it. For a new enclosure, compare the wider choices in best NAS for home.

What 20 TB per disk actually gives you

Using QTS's RAID definitions, two 20 TB disks in RAID 1 give 20 nominal TB; four in RAID 5 give 60 nominal TB; four in RAID 6 give 40 nominal TB. These are calculated capacities before formatting, system allocations, snapshots and reserves.

• 20TB nominal mirrored capacity from two 20 TB disks
• 60TB nominal RAID 5 capacity from four 20 TB disks
• 40TB nominal RAID 6 capacity from four 20 TB disks

Decimal TB and binary TiB also differ: convert using TB × 10^12 ÷ 2^40. Seagate defines TB as a trillion bytes; NIST defines the binary prefix. A smaller binary display is expected before other overhead. Size the backup for live data plus retained versions and growth, rather than treating nominal capacity as a fill target.

A complete drive-and-backup order

For this worked example, order a QNAP TS-464-8G, four identical supported 20 TB drives, a QNAP TR-004, and four more identical supported 20 TB drives. An optional matching spare is additional to the installed sets.

The TS-464 has four bays, built-in 8 GB memory, two 2.5GbE ports and QTS by default; drives are sold separately. Configure its main array as RAID 6, giving 40 nominal TB. This is our editorial preference here for its two-disk failure tolerance, not a claim that every home needs that layout.

The TR-004 is a four-bay USB enclosure with hardware RAID, not a standalone network server. Configure its separate backup array as RAID 5, giving 60 nominal TB: extra nominal room for version history compared with the main array, though retention still needs monitoring. It supports RAID 5, but not RAID 6. Its manual includes a power adapter and USB Type-C-to-Type-A cable; connect it directly to the NAS, without a hub. Confirm the NAS power supply and network cable in the selected package too.

Use the TR-004 in external storage mode for a separate backup, rather than treating expansion space as another copy. QNAP explicitly documents that role. In HBS 3, create a Backup & Restore → New backup job, select the protected folders and external destination, and configure version retention. Restore sample files before relying on the job; keep an off-site copy of irreplaceable data. Budget space for every protected folder, not only the media share.

Replace drives in the supported order

For QTS 5.2.x, QNAP documents expansion by replacing every member of RAID 1, 5, 6 or 10 with a larger drive. Mixed-capacity redundant groups use the smallest member's capacity: swapping only one old disk for 20 TB does not deliver the full-array increase. Check your actual OS instructions before changing anything.

Follow QNAP's replacement procedure, after verifying an independent backup:

1. 1

   Confirm recovery

   Verify a backup and restore sample files before starting.

2. 2

   Replace one member

   Use Manage → Replace Disks One by One and follow the removal prompt.

3. 3

   Wait for each rebuild

   Do not remove another disk while the group is rebuilding.

4. 4

   Expand after the whole set

   After every member has been replaced and rebuilt, use Expand Capacity; then check pool and volume allocation.

The TR-004 is different: its manual says it supports neither capacity expansion nor RAID-level migration. Plan a separate verified copy, recreation of its array and restoration when increasing its capacity. Do not apply the NAS's online replacement sequence to that enclosure.

Black Friday drive sets and the 30 TB alternative

When comparing Black Friday hard drive deals or Cyber Monday offers, make the basket identical: model suffix, SATA interface, drive count, new-retail condition, regional warranty and recovery eligibility. Check who actually handles replacement. A recertified, used or OEM offer needs its own written terms; do not carry the new-drive warranty across by family name. WD explicitly notes that recertified units may be repaired customer returns.

That 30 TB drive is not inherently unsupported in this example. The trap is expecting one larger member to increase a redundant pool still limited by 20 TB members, or expecting the TR-004 to grow its existing RAID group. Recalculate the whole set and backup destination before accepting a substitution. A holiday label establishes neither suitability nor warranty eligibility.

Verdict

Start with ST20000NT001 for its documented workload and included Rescue term, or WD202KFGX when its exact support entry and warranty route suit you better. Buy only after the NAS, backup destination and replacement procedure all match. For the worked QNAP set, our preference is a RAID 6 primary array and a separate, larger nominal RAID 5 backup array, with capacity left for retained versions.