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Western Digital 18TB UltraStar DC HC550 Review

Rapacious storage demands in the data center are putting hard disk manufacturers under extreme pressure to deliver ever greater capacities. And they’re stepping up to the plate as although it didn’t seem that long ago that Seagate, Western Digital (WD) and Toshiba launched 16TB data center class hard disk drives (HDDs), we now have production 18TB drives in the lab.

In this review, we look at WD’s mighty 18TB UltraStar DC HC550 model number WUH721818ALE6L4 which has a keen focus on a range of data center applications including Big Data analytics, cloud and hyperscale storage, massive scale-out and distributed file systems. Available with SATA III or SAS3 interfaces, the DC HC550 employs a range of innovative technologies aimed at improving reliability, performance and power consumption – and one that’s a little bit mysterious.

Ultrastar DC HC550 Hard disk features

18TB UltraStar DC HC550 model number WUH721818ALE6L4The UltraStar DC HC550 18TB is designed specifically for massive, rack dense storage arrays. It has none of the limitations enforced on WD’s Red NAS drives where the Plus models support up to 8-bay appliances while the Pro pushes this to a maximum of 24 bays.

As expected, the DC HC550 drives are helium filled and WD’s HelioSeal technology ensures they stay completely sealed and contaminant-free. First introduced in 2013, HelioSeal hermetically seals the hard disk chassis thus avoiding issues common with air-filled drives which usually require a breather hole in their casing.

By using helium instead of air inside the drive, HelioSeal is able to decrease turbulence and buffeting allowing the actuator arms to be more precisely positioned as vibration and platter movement at high revolutions are significantly reduced. Another benefit of the helium’s reduced drag is less power is required for the spindle motor with WD claiming its 18TB drives consume 22% less power in idle than its 14TB models.

The DC HC550 uses TDMR

Click to enlarge (Image credit: WD)

The DC HC550 uses TDMR (two dimensional magnetic recording) heads but WD has introduced new drive mechanics and a suite of new features. The drive uses nine platters and the various technologies that deliver increased areal density have allowed WD to store 2TB on each platter.

WD claims an industry first as the DC HC550 employs a new triple stage actuator (TSA). By using three pivot points, TSA can position the read-write heads more accurately on tracks allowing them to be placed closer together resulting in more tracks per inch (TPI) and the greater areal density.

Manufacturers have been developing a number of technologies to increase HDD capacity with the two main ones being MAMR (microwave assisted magnetic recording) and HAMR (heat assisted magnetic recording). Collectively grouped under the EAMR (energy assisted magnetic recording) heading, WD discovered during its research a feature it has called ePMR (energy assisted perpendicular magnetic recording).

WD EAMR technology

Click to enlarge (Image credit: WD)

For competitive reasons, WD is a little coy about which EAMR technology it comes from, but ePMR sends an electrical current to the write head to produce an additional magnetic field. Without getting technical, it allows BPI and aerial density to be increased by producing a more consistent write signal and significantly reduced jitter.

Vibration in multi-drive storage arrays and appliances running 24/7 operations can be a major issue as hard disks in close proximity to each other can accelerate hardware failures and errors. The DC HC550 counters this with a set of well-established technologies including top and bottom attached spindle motors.

WD’s standard rotational vibration safeguard (RVS) technology uses sensors placed on the edges of the hard disk’s circuit board to detect vibration ‘ripples’. The sensors signal this to the drive’s actuator allowing it to compensate by controlling the head position and effectively countering the vibration and stabilizing the head position.

Lab test setup

The UltraStar DC HC550 is designed for use in multi-drive RAID arrays so, for real-world performance testing, we used QNAP’s TVS-882BR. This 8-bay high-end desktop appliance is equipped with a 3.6GHz quad-core Intel Core i7-7700 CPU and 32GB of DDR4 memory.

ATTO Celerity FC-164P HBA with quad 16Gbps FC ports + QNAP’s TVS-882BR + 4 x 18TB WUH721818ALE6L4

The QTS system software and apps were loaded on a dedicated mirrored array comprising two enterprise-class 1.92TB Micron 5200 Max SATA SSDs. For performance testing, we fitted four 18TB DC HC550 SATA models and created a dedicated 49TB RAID5 storage pool.

With QTS providing fibre channel support as standard, we opted to use this for high-performance testing and installed an ATTO Celerity FC-164P HBA with quad 16Gbps FC ports in the appliance. Our test host was a Dell PowerEdge T640 tower server equipped with dual 2.1GHz 22-core Xeon Scalable Gold 6152 CPUs, 384GB of DDR4 plus an ATTO Celerity FC-164P HBA and running Windows Server 2019.

We created a dedicated 1TB FC LUN on the test drive array and mapped it to the server over a dual-port 32Gbps MPIO FC connection. Tests were conducted using Iometer configured with 256KB transfer request sizes for testing maximum sequential and random read/write rates and 4KB request sizes to measure IOPS throughput.

Ultrastar DC HC550 Performance analysis

Testing the UltraStar DC HC550 drives in a RAID array and over high-performance fibre channel connections to a host system allowed us to see how they behave in a real world business environment. Also, this is the same lab environment used to test the 16TB data center drives from Seagate and Toshiba so we could directly compare performance results.

Overall, we found the DC HC550 performed very well with it delivering some impressive results. In our Iometer sequential read tests, the DC HC550 delivered top speeds of 3,150MB/sec – almost identical to the Exos X16 and MG08 drives. Sequential write performance was a little lower with the array returning steady speeds of 3,125MB/sec – between 10-14MB/sec slower than Seagate and Toshiba.

There were no appreciable differences for random read performance with the DC HC550 delivering a steady 3,149MB/sec. Our 100% random write test is a worst-case scenario as few businesses will have these kinds of workloads but we found the DC HC500 offered comparatively good speeds.

Ultrastar DC HC550 18TB 32Gbps Fibre Channel

The DC HC550 array also returned excellent results in our throughput tests and in some cases, pulled ahead of Seagate and Toshiba. Sequential read and write rates held steady at 299,800 IOPS and 233,600 IOPS while random read and write tests returned 297,900 and 3,350 IOPS.

Ultrastar DC HC550 18TB 32Gbps IOPS


WD’s 18TB DC HC550 SATA hard disk sets a high standard for the rest to follow. This 7,200rpm drive claims the same 2.5M hour MTBF as its 16TB competitors, backs it up with a 550TB yearly workload rating and is protected by a 5-year limited warranty.

The claimed single drive performance of 269MB/sec is marginally higher than Seagate’s Exos X16 and Toshiba’s MG08 which quote 261MB/sec and 262MB/sec respectively. In our real-world RAID tests, the DC HC550 delivered very good results and returned noticeable improvements in IOPS for our sequential and random read and write throughput tests.

The DC HC550 also introduces a number of technology firsts for WD with its TSA aimed at improving overall reliability and track density. Traditional PMR (perpendicular magnetic recording) technology is reaching the upper limits of capacities but WD’s ePMR ‘extension’ has allowed it to increase capacity without needing to design new disk heads

WD’s UltraStar DC HC550 is a great choice for mid-range businesses, enterprises and data centers running mission-critical services that want a solid combination of performance and reliability. Its high capacity lends itself well to a wide range of enterprise-class workloads, it delivered great results in our lab performance tests and at $495, is competitively priced.

WD WUH721818ALE6l4 Ultrastar DC HC550 18TB
7200RPM SATA-6Gb/S, 512MB Buffer, 512e Se 3.5inch Helium Platform Enterprise Hard Drive
Western Digital 18TB UltraStar DC HC550 Review
9.3 Total Score
Leader of the Pack

WD’s 18TB DC HC550 SATA hard disk sets a high standard for the rest to follow. This 7,200rpm drive claims the same 2.5M hour MTBF as its 16TB competitors, backs it up with a 550TB yearly workload rating and is protected by a 5-year limited warranty.

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