DatacenterDisk

WD Ultrastar vs Western Digital WD

Side-by-side spec and price comparison. Live data from Amazon US.

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Our Recommendation
👑
WD Ultrastar 7K4000 4TB SATA NAS

WD Ultrastar 7K4000 4TB SATA NAS offers the best value at $47.50/TB. Available new with manufacturer warranty.

Best $/TB: WD
Best Warranty: Western Digital
Best for RAID: WD
Full Specification Comparison
Spec
WD
Ultrastar 7K4000 4TB SATA NAS
$47.50/TB
Western Digital
WD Purple 4TB WD40PURX
$55.50/TB
Brand
WD
Western Digital
Model
Ultrastar 7K4000 4TB SATA NAS
WD Purple 4TB WD40PURX
Series
Ultrastar
WD Purple
Part Number
HMS5C4040ALE640
WD40PURX
$/TB
👑$47.50
$55.50
Price
$190.00
$222.00
Condition
New
New
Capacity
4TB
4TB
Interface
SATA-6G
SATA-6G
Form Factor
3.5"
3.5"
Drive Type
HDD
HDD
Recording Tech
CMR
—
RPM
7,200
N/A (SSD)
Cache
—
—
Sector Size
512n
—
Workload Rating
—
—
DWPD
N/A
N/A
Warranty
—
—
Workload Tier
nearline
—
In Stock
✓ In Stock
✓ In Stock
Buy
Buy on Amazon →
Buy on Amazon →
Workload Fit
Workload
WD
Western Digital
NAS Storage
●●●
●●●
Backup Target
●●●
●●●
OLTP Database
●
●
Cold Archive
●
●
Virtualization
●
●
AI/ML Storage
●
●
Buying Recommendation
Choose WD Ultrastar 7K4000 4TB SATA NAS if:
  • ✓ You need maximum storage per dollar
  • ✓ You're building a RAID array and need guaranteed CMR compatibility
  • ✓ You need new-with-warranty for compliance or budgeting
Buy WD →
Choose Western Digital WD Purple 4TB WD40PURX if:
  • ✓ You need new-with-warranty for compliance or budgeting
Buy Western Digital →

Frequently Asked Questions

WD Ultrastar offers better value at $47.50/TB vs $55.50/TB - a 14% price difference. Factor in warranty length and workload rating when the price gap is small.

Mixing drives of different models in RAID is not recommended even if capacities match. Different firmware, error handling and seek patterns can cause rebuild issues. Use identical drives within the same RAID group for reliable operation.

Both drives carry similar warranty terms and are built for enterprise operation. Check brand-specific AFR data and Backblaze drive stats for real-world failure rate comparisons.

WD Ultrastar is the better fit for NAS storage. It uses CMR recording which is safe for all RAID levels. SATA interface is compatible with all NAS platforms including Synology, QNAP and TrueNAS.