WD 4TB HGST UltraStar 0B35950 7200R 256MB Cache 5Y


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Western Digital HGST Ultrastar 0B35950 4TB 256MB 7200RPM SATA 6Gb/s 3.5In 5YR

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SKU: HD1WD1HD5008 Category: Tag:


Ultrastar 7K6

Economics and Access Speed: Key Requirements for Low Capacity HDDs in the Data Center
As the industry evolves to develop purpose-built solutions for growing data storage requirements, IT managers continue to rely on lower capacity drives that are economical to acquire, yet deliver quick and reliable data access for traditional data center applications. Ultrastar® 7K6 is a low-capacity HDD, with 6TB and 4TB offerings, that helps address economic and access requirements of many traditional IT workloads. Low capacity drives also help address architecture limitations. The Ultrastar 7K6 is designed for traditional storage and server applications as well as distributed and scalable computing, including block and file storage architectures, providing fast 7,200 RPM performance and lower acquisition cost to help ease budget constraints. Ultrastar 7K6 is offered with either 6Gb/s SATA or 12Gb/s SAS interface in a choice of 512e or 4Kn formats. A 512n option is also available on 4TB models to support legacy systems with native 512-byte block sizes.

Technology Innovation Delivers Efficiency and Performance for Traditional and Legacy Systems
Ultrastar 7K6 is based on a new 4-disk air platform design that uses conventional magnetic recording (CMR) technology in a 3.5-inch large form factor. Compared to the prior generation, Ultrastar 7K6000, the 7K6 delivers a 12% performance boost and uses slightly larger-diameter media. It features a second-generation, dual-stage micro actuator to enhance head positioning accuracy for better drive performance. Write performance gains are also supported by Western Digital’s media cache architecture, a disk-based caching technology that provides a large cache area on the disk, which also improves reliability and data integrity during unexpected power loss. Finally, the addition of flash-based non-volatile cache (NVC) on both SATA and SAS models helps improve write performance. The Ultrastar 7K6 also includes a Rebuild Assist feature, which helps dramatically reduce RAID rebuild times and maintain system performance during the rebuild process. Learn more in our Rebuild Assist technical brief.

Data Security with Trusted Quality, Reliability
Compliance and privacy requirements drive the need for increased data security. Ultrastar 7K6 helps protect data from unauthorized use by offering security and encryption options. SAS models offer hardware-based encryption options, including a Trusted Computing Group (TCG) Enterprise_A, TCG with FIPS 140-2 certification, Level 2. The Ultrastar 7K6 extends Western Digital’s long-standing tradition of reliability leadership with a 2M-hour MTBF2 rating.

Features & Benefits


  • Feature / Function
    • 6TB & 4TB
    • Advanced Format up to 6TB
    • 512n format available on 4TB
  • Benefits
    • Lower capacity points needed for traditional IT workloads and applications
    • Enables higher capacities and reliability
    • Compatibility with legacy systems


  • Feature / Function
    • Non-volatile cache (NVC)
    • Up to 255MB/s transfer rate (512e/4Kn); 233MB/s transfer rate (512n)
  • Benefits
    • Improved write performance and write splice protection
    • 12% faster than prior generation


  • Feature / Function
    • Dual-stage Micro Actuator
    • 2M hours MTBF and 0.44% AFR
  • Benefits
    • Better head positioning and rotational vibration robustness
    • One of the highest reliability ratings for air-filled Capacity Enterprise HDDs


  • Excellent random and sequential performance
  • 6TB and 4TB capacity points support traditional IT systems
  • Sustained transfer rate up to 255MB/s (512e/4Kn models); 233MB/s (512n models)
  • Choice of 12Gb/s SAS or 6Gb/s SATA
  • Advanced Format 4Kn and 512e models up to 6TB; 512n formatting available on 4TB to support legacy systems
  • Self-Encrypting Drive (TCG SAS) options

Applications & Workloads

  • Distributed file systems, like Apache Hadoop®, to support Big Data analytics
  • Direct & Network Attached Storage (DAS & NAS)
  • RAID arrays
  • Legacy applications requiring 512n format (4TB)
Model Number 0B35950
Data Security Mode Secure Erase (overwrite only)
Interface 512n SATA 6Gb/s
Power Disable Pin 3 status Legacy Pin 3 config – No Power Disable Support)
Interface SATA 6Gb/s
Capacity 4TB / 4000GB
Form Factor 3.5-inch
Sector size (bytes) 512n:

  • 512
Max. areal density (Gbits/sq. in., max) 512e/4Kn:

  • 782
  • 696


  • 753
Data buffer (MB) 256
Rotational speed (RPM) 7200
Latency average (ms) 4.16
Interface transfer rate (MB/s, max) 1200
Sustained transfer rate

  • (MiB/sec, typ.)
  • (MB/sec, typ.)
  • 512e/4Kn: Up to 243
  • 512n: 222
  • 512e/4Kn: Up to 255
  • 512n:
  • 233
Seek time (read/write, ms, typ.) 8.0/8.6
Error Rate (non-recoverable bits read) 1 in 10e15
Load/Unload cycles (at 40°C) 600,000
MTBF2 2M hours
Annual failure rate (AFR) 0.44%
Availability (hrs/day x days/wk) 24×7
Idle/Operating (Bels, typical) 2.9/3.6
Requirement (+/- 5%) +5V, +12V
Operating (W, typical)
  • 12
Idle (W)8 7.0
z-height (mm, max) 15
Dimensions (width x depth, mm) 70.1 x 100.6
Weight (g, max) 715
Environmental (operating)
Ambient Temperature 0º to 60º C
Non-operating Temperature -40º to 80º C
Shock (half-sine wave, G) 70
Vibration (G RMS, 2 to 200 Hz) 0.67
Environmental (non-operating)
Ambient Temperature -40°C to 70°C
Shock (half-sine wave, G) 300
Vibration (G RMS, 5 to 500 Hz) 1.04

Additional information

Weight 2 lbs
Dimensions 6 × 10 × 4.25 in