WD Ultrastar DC HC550 16TB
16TB
Model WUH721816ALE6L4
- rpm
- 7,200
- MB cache
- 512
- TB/yr
- 550
- yr warranty
- 5
WD Ultrastar DC HC550 range
Should you buy the WD Ultrastar DC HC550 16 TB?
It makes most sense when you're chasing terabytes per pound and the NAS sits somewhere noise doesn't matter. Think garage, or a rack in the cupboard under the stairs. WD backs it for five years, which is a long time in drive terms. Backblaze's numbers are on its side as well, with 0.54% lifetime AFR over 84,197 drive-years and even the top of the 95% interval under the 1.40% median. It's CMR, which is what you want anywhere near a RAID or ZFS rebuild.
Watch out for
At 7,200 rpm it's from the louder, warmer class. Fine in a cupboard, less fun on a desk.
Put four in RAID 5 and you'll have 48 TB to fill (Windows will call it 43.7 TB).
Specifications
Each value links to the Western Digital page or datasheet it came from, and "Not published" means the maker doesn't list it there.
| Capacity | 16 TB | source for Capacity (documents.westerndigital.com, opens in new tab) |
|---|---|---|
| Spindle speed | 7,200 rpm | source for Spindle speed (documents.westerndigital.com, opens in new tab) |
| Recording technology | CMR | source for Recording technology (documents.westerndigital.com, opens in new tab) |
| Cache | 512 MB | source for Cache (documents.westerndigital.com, opens in new tab) |
| Interface | SATA 6Gb/s | source for Interface (documents.westerndigital.com, opens in new tab) |
| Form factor | 3.5in | source for Form factor (documents.westerndigital.com, opens in new tab) |
| Workload rating | 550 TB/yr | source for Workload rating (documents.westerndigital.com, opens in new tab) |
| MTBF / MTTF | 2,500,000 hours | source for MTBF / MTTF (documents.westerndigital.com, opens in new tab) |
| Warranty | 5 years | source for Warranty (documents.westerndigital.com, opens in new tab) |
Sources: documents.westerndigital.com
Failure rate
Backblaze has 26,208 of them in service as WDC WUH721816ALE6L4. They've clocked up 84,197 drive-years between them and 452 have died, which puts the lifetime AFR at 0.54% (95% interval 0.49% to 0.59%, comfortably under the 1.40% median for the drive models they report).
Lifetime84,197 drive-yrs 0.54%0.49–0.59
2025 Q326,349 drives 0.96%0.74–1.23
2025 Q426,310 drives 0.66%0.48–0.89
2026 Q126,263 drives 0.86%0.65–1.12
2026 Q226,208 drives 1.13%0.89–1.42
Median lifetime AFR across Backblaze drive models: 1.40%
Source: Backblaze Drive Stats, lifetime to 2026 Q2. Bear in mind that's data-centre use, which is a lot harder on a drive than a home NAS will ever be.
Backblaze also reports this drive under WUH721816ALE6L4 (531 drives, 4.91% AFR, CI 3.08%–7.43%). The chart uses the bigger fleet.
WD Ultrastar DC HC550 16TBWUH721816ALE6L4