Drive comparison
ST18000NM000J vs WUH721818ALE6L4
Seagate Exos X18 18TB and Western Digital Ultrastar DC HC550 18TB, compared using published manufacturer specifications.
Seagate
Exos X18 18TB
ST18000NM000J
SATA 6 Gb/s · 3.5-inch
$725.91
Amazon US · New listing ↗ASIN B08JV6PP9B · as of Sep 12, 2026 11:43 UTC
Full specifications & all listings →
Western Digital
Ultrastar DC HC550 18TB
WUH721818ALE6L4
SATA 6 Gb/s · 3.5-inch
$529.00
Amazon US · Used / renewed listing ↗ASIN B09RYLD7GL · as of Sep 12, 2026 04:47 UTC
Full specifications & all listings →As an Amazon Associate I earn from qualifying purchases. Match the selected variant, condition and seller terms before ordering.
What differs between these models?
- Cache (MB): ST18000NM000J lists 256; WUH721818ALE6L4 lists 512.
A larger cache, higher RPM or higher advertised sequential speed alone does not establish which drive is better for your workload.
Specifications side by side
| Specification | ST18000NM000J | WUH721818ALE6L4 |
|---|---|---|
| Manufacturer | Seagate | Western Digital |
| Product family | Exos X18 | Ultrastar DC HC550 |
| Model number | ST18000NM000J | WUH721818ALE6L4 |
| Capacity (TB) | 18 | 18 |
| RPM | 7200 | 7200 |
| Interface | SATA 6 Gb/s | SATA 6 Gb/s |
| Cache (MB) | 256 | 512 |
| Form factor | 3.5-inch | 3.5-inch |
| Average idle power (W) | 5.3 | Not recorded |
| Power-on hours per year | 8760 | Not recorded |
| Manufacturer limited warranty | 5 years (eligible new drives) | Not recorded |
| Sustained transfer (up to MB/s) | 270 | Not recorded |
| Sector format | Not recorded | 512e |
| Drive construction | Not recorded | Helium |
| Power Disable Pin 3 | Not recorded | Not supported (legacy configuration) |
Compatibility and buying checks
- Check sector-format support in the controller and operating system, particularly for native 4K (4Kn) variants.
- Compare new and renewed offers separately. The manufacturer specification does not guarantee the warranty or return policy of a marketplace seller.
Manufacturer sources
ST18000NM000J
Seagate Exos X18 manufacturer specifications ↗ · pages 2
Reviewed 2026-09-07. Published specifications; no independent benchmark or failure-rate claim.
WUH721818ALE6L4
Western Digital Ultrastar DC HC550 datasheet ↗ · pages 2
Reviewed 2026-09-07. Published specifications; no independent benchmark or failure-rate claim.