Seagate

Seagate Exos X20 18TB SATA

ST18000NM003D
Exos XnearlineePMR18TBSATA-6G3.5"
$37.55/TB
$675.89
newIn Stock
Price updated
Price accurate as of Aug 31, 2026, 03:01 AM
Buy on Amazon →

The Seagate Exos X20 18TB SATA is a 18TB SATA-6G HDD in new condition. It is in stock at $675.89 - $37.55/TB.

Part number: ST18000NM003D — decoded, with sibling variants and the warranty check.

Same capacity, other options
DriveInterfaceCond$/TBPrice
MDD 18TB SATA 6G 7200RPM NASSATA-6GRefurb$25.00$449.99Buy
MDD 18TB SATA 7200RPM NASSATA-6GRefurb$25.56$459.99Buy
MDD 18TB SATA 7200RPM EnterpriseSATA-6GRefurb$26.11$469.99Buy
WD WD Purple 18TB WD180PURZSATA-6GRefurb$28.64$515.49Buy

All 18TB drives we track, ranked by cost per terabyte.

Model context

Part of the Seagate line we track.

Quick Verdict

The Seagate Exos X20 18TB SATA is a 18TB SATA-6G enterprise drive at $37.55/TB - CMR recording makes it safe for all RAID levels and NAS deployments. New unit with full 5-year warranty.

Share:WhatsAppFacebookPost on X

Specifications

Capacity18TB
Form Factor3.5"
InterfaceSATA-6G
Recording TechePMR
RPM7200
Cache256MB
Sector Size512e
Workload Rating550TB/yr
Warranty5 years
ASINB09MWLJ1P5
Market context

Against every other drive we have an in-stock price for today, this one is cheaper per tb than 66% of them (163 of 247). The cheapest we can currently buy is $14.99/TB; the middle of the market is $36.67/TB.

Where the wider market has moved

These are third-party figures about the retail market as a whole, quoted and dated. They are not our own measurements and they do not describe this specific drive.

Compare against every 18TB drive we track →Cheapest per terabyte, all categories →Category price trends →
How it compares - 18TB SATA-6G
#1WD Ultrastar DC HC550 18TB SATA
$17.17/TB
#2Toshiba MG09 18TB SATA Enterprise
$20.56/TB
#3Toshiba MG09 18TB SATA
$22.22/TB
#4MDD 18TB SATA 6G 7200RPM NAS
$25.00/TB
#5MDD 18TB SATA 7200RPM NAS
$25.56/TB

Works in these NAS machines

QNAP TS-664
Vendor-listed
On QNAP's TS-664 list as Enterprise EXOS x20 ST18000NM003D
QNAP TS-673A
Vendor-listed
On QNAP's TS-673A list as Enterprise EXOS x20 ST18000NM003D
Asustor (8 NAS series)
Vendor-listed
On Asustor's list as Exos X20 ST18000NM003D
UniFi UNAS / UNVR
Fit-verified
Meets Ubiquiti's written 1TB+ CMR requirement; check the 7200RPM clause

Resolved against manufacturer compatibility lists we read and dated, capped at 4. Vendor-listed means the manufacturer names this exact part number; fit-verified is our own check of form factor, interface and recording technology against a published requirement. Neither is a guess, and a drive the registry cannot resolve shows nothing here rather than a maybe. How compatibility actually works

Frequently Asked Questions

Yes. The Exos X20 18TB SATA uses ePMR recording which is fully compatible with all RAID levels. It is rated for 550TB/year workload.

5-year manufacturer warranty.

Compatible with any server, NAS or workstation with a SATA port. Works in Synology, QNAP, TrueNAS, UnRAID and all major NAS platforms.

Use Case Scenarios

🏠
Home & SMB NAS
Building a high-capacity NAS for media, backups and file sharing.
✓ Excellent fit
CMR recording is RAID-safe and fully compatible with Synology, QNAP, TrueNAS and UnRAID. New drives come with full warranty.
💾
Backup Server / Veeam Target
Dedicated backup storage for Veeam, Commvault, or NetBackup.
✓ Excellent fit
18TB SATA drives are ideal for backup targets. SATA gives maximum $/TB for backup repositories.
☁️
Object Storage / Cold Data Tier
High-density storage for MinIO, Ceph or Hadoop at scale.
✓ Excellent fit
At 18TB per drive, a 60-bay JBOD delivers 1080TB raw — enough for petabyte-scale object storage.

Maintenance & Troubleshooting

Maintenance Checklist

On installCheck SMART baseline on arrival
Run smartctl -a /dev/sdX and record: Reallocated_Sector_Ct, Power_On_Hours, Spin_Retry_Count. Establishes baseline for future comparison.
MonthlyRun SMART short self-test
smartctl -t short /dev/sdX — takes 1-2 minutes, catches most developing issues. Schedule during off-peak.
QuarterlyRun SMART long self-test
smartctl -t long /dev/sdX — full surface scan, takes 9 hours for 18TB. Any test failure is grounds for immediate replacement.
QuarterlyCheck RAID array health
Verify no degraded drives. A degraded array with no hot spare is one failure from data loss. Check mdstat or controller UI.
AnnuallyVerify drive firmware version
Check Seagate support site for firmware updates. Some versions have known bugs affecting integrity.
Every 3-5 yearsPlan proactive replacement
Enterprise HDDs have higher failure rates after year 4-5. At 18TB per drive, budget for replacements before failures occur.

Troubleshooting Guide

Cause: Loose SATA data or power cable, failed port, or drive not spinning up.
Fix: Reseat both cables. Try a different port. Listen for spin-up sound. Test with a known-good cable.