Western Digital · Data-centre drive · HUH721212ALE604
WD Ultrastar DC HC520 12TB
WD builds this one for data-centre racks; in a home NAS it's simply a big 7,200 rpm SATA drive with five years' cover.
- Capacity
- 12 TB
- Recording
- CMR
- Speed
- 7,200 rpm
- Warranty
- 5 years
- Workload
- 550 TB/yr
- Failure rate
- AFR 1.77% high
Good for
- Busy arrays (550 TB a year)
- Big media libraries
- RAID, SHR and ZFS rebuilds
- 5 years' warranty
Not for
- A desk or bedroom (7,200 rpm is the louder class)
- Anyone who goes by Backblaze’s numbers
Updated 27 Oct 2026 · Method 2.0
Who the WD Ultrastar DC HC520 12 TB is for
It's at home in a rack or a garage, where 7,200 rpm of spinning rust can whirr away all day without bothering anyone. You also get five years' warranty, two more than the cheapest NAS lines. It's CMR, which is what you want anywhere near a RAID or ZFS rebuild.
Watch out for
It's a 7,200 rpm drive and you'll hear it working. Reliability's the question mark. Backblaze has it at 1.77% lifetime AFR, and the interval doesn't reach down to the 1.38% median.
WD's datasheet puts it at 20 dB idle and 36 dB seeking. Power draw is 5 W idle and 6.9 W working on WD's figures, or 44 kWh a year if it spends the whole year idling. A 4-bay box full of these gives 36 TB after one drive's worth of parity.
Specifications
Each value links to the Western Digital page or datasheet it came from.
Sources: documents.westerndigital.com
Failure rate
1,224 failures in 69,066 drive-years, across the 13,057 that Backblaze runs as HGST HUH721212ALE604, works out at 1.77% a year. Its 95% interval is 1.67% to 1.87%, and even the bottom of that is over the 1.38% median.
Median lifetime AFR across Backblaze drive models: 1.38%
Source: Backblaze Drive Stats, lifetime to Q2 2026. Bear in mind that's data-centre use, which is a lot harder on a drive than a home NAS will ever be.