Compare a specific generation and interface
Exos and Ultrastar are broad enterprise brands, not single drives. This comparison narrows the choice to standard SATA Exos X18 models and SATA base HC550 models at 14TB, 16TB and 18TB. Other generations, SAS versions and encryption variants can have different specifications. There is no defensible family-wide reliability ranking in this guide.
The SATA model numbers to compare
The table pairs equivalent nominal capacities. Exos models ending NM000J in this shortlist use SATA, while other X18 suffixes include SAS models. For HC550, the ALE6L4 suffix identifies the SATA base variant with legacy Pin 3 configuration in WD’s model-number guide. A drive’s physical size does not establish electrical or controller compatibility.
Sector format and power behaviour need an explicit check
Seagate documents FastFormat 512e/4Kn for the listed X18 models. The HC550 ALE6L4 entries here are 512e SATA models. If the drive joins an existing array, check what formats the controller and software support. Enterprise families also have differing Power Disable configurations. Consult the exact manual and enclosure documentation rather than following an improvised power-cable workaround.
Renewed value depends on the offer
An enterprise datasheet describes the original hardware. It does not tell you the history, power-on hours or remaining service life of a renewed unit. Compare seller identity, return terms, who handles the warranty and whether testing is documented. A low price for a SAS variant is not a useful substitute when your system accepts SATA only.
Which should you buy?
Choose among exact models your system supports, then compare the total cost and terms of equivalent offers. If the models meet the same workload requirements, seller support and return coverage can matter more than a brand-level specification difference. Keep an independent backup and allow time to test an empty drive before its return window closes. We have not tested these drives’ noise, failure rates or sustained performance side by side.
Quick Decision Guide
| Capacity | Exos X18 SATA | Ultrastar HC550 SATA |
|---|---|---|
| 14TB | ST14000NM000J | WUH721814ALE6L4 |
| 16TB | ST16000NM000J | WUH721816ALE6L4 |
| 18TB | ST18000NM000J | WUH721818ALE6L4 |
Frequently Asked Questions
Are these recommendations based on Disk Scout benchmark testing?
Does a manufacturer warranty apply to a renewed offer?
Sources
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