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Western Digital 18TB Ultrastar DC HC550 Hard Drive
Related: diglloydTools, hard drive, Other World Computing, OWC Mercury Elite Pro, RAID, SSD, storage, Toshiba, USB
This page evaluates the Western Digital 18TB Ultrastar DC HC550 hard drive for speed across the entire volume capacity as well as speeds for 32K to 512MB transfers.
The OWC Mercury Elite Pro USB 3.2 enclosure was used to house the drive. It is a fanless, USB 3.2, all-aluminum proven performer.
18TB Ultrastar DC HC550 hard drive
- CMR technology works with all capacity enterprise applications & environments
- Reliable, field-proven, 6th generation design
- Industry’s first HDD with Energy-Assisted Magnetic Recording technology
- HelioSeal® design delivers outstanding power efficiency
- 2.5M hours (projected) MTBF2 rating
About hard drive performance
Hard drives slow down as they fill up. The outer tracks deliver more data per rotation than more inward inner tracks due to constant data density, but a much greater circumference in the outer tracks—more data per revolution of the platters. Thus performance drops steadily as the slower and slower inner tracks are used. This is true of ALL hard drives, but not SSDs.
TIP #1: to sustain higher performance for same capacity utilization, buy larger hard drives.
Creating a volume using less than the full capacity bounds that volume’s storage area to the faster tracks (first volume created gets the outer and fastest tracks, next volume gets the next-fastest tracks, etc).
TIP #2: to guarantee minimum performance for a fixed-size capacity, the first partition/volume will be the fastest. Use less than the full capacity to guarantee a bounded minimum speed e.g., a 12TB partition on a 16TB total capacity. The extra space can be ignored, or used for a 2nd much slower volume.
$349 SAVE $450 = 56.0% Western Digital 18TB ULTRASTAR DC HC550 3.5 inch Enterprise SATA… in Storage: Other
Test results: Speed across 18TB capacity
Test mule was the 2019 iMac 5K. While it uses USB 3.1, the 5Gpbs is still more than ample to support maximum hard drive speed for a single drive.
For over 12 years, DiskTester has been the best means available to ascertain how a drive performs across its capacity. When working with RAID, graphing each hard drive individually can reveal performance irregularities that can cause hiccups in RAID performance when multiple drives are used—problem drives can be swapped out for better ones.
Hard drives slow down as they fill up, so a key way to evaluate hard drive is by its average speed across its capacity, as well as how it performs at around 80% capacity usage.
On the fastest part of the volume, speed is blistering-fast for a hard drive, around 276 MB/sec.
At 50% capacity speed is down to about 235 MB/sec—still very fast for a hard drive.
At 80%, about 180MB/sec—superb, since that is ~14.7TB of capacity usage.
Fantastic! This is the fastest hard drive MPG has ever tested as of early 2021.
Past 80% capacity, speed falls off to 126 MB/sec at the very limits of the capacity.
The ~80%-full metric (14.4TB in use) is a good one, as it is roughly at 14TB hard drives. Most impressive is that at 14TB capacity usage, the Western Digital 18TB is 55% faster than the Toshiba 14TB (~120MB /sec for the Toshiba 14TB vs 187MB/sec for the WD18).
In other words the WD 18TB hard drive is a far higher performance 14TB hard drive than the Toshiba 14TB hard drive. Buy it for its full capacity or buy it as a super-fast 14-15TB drive.
Average Write speed: 226 MB/sec
Average Read speed: 227 MB/sec
Vertical scale is MB/sec. Horizontal scale is percentage of volume capacity — 50% of 18TB volume is 9TB of capacity.
The fill-volume command of diglloydTools Disktester was used for this data with 128MB transfer size.
NOTE: title of chart is a typo; it is across the entire 18TB capacity.
Tested later with a 2nd sample in the OWC Mercury Elite Pro Dual USB-C, the two samples have identical write speeds, and nearly identical read speeds. This is as tight a performance as MPG has ever seen for hard drives—superb, and ideally suited for RAID.
To nitpick a little, peak performance is a little bit lower than the single-drive performance above, and the Dual enclosure is a bit slower for writes than for reads.
Test results: speed vs transfer size
Test mule was the 2019 iMac 5K.
Early on in testing, it became clear that the Western Digital 18TB hard drive had superb caching with its huge 512MB onboard cache. Transfer performance for 32K and 64K transfers is as good as some SSDs. And by 128K full performance is reached and maintained thereafter—mighty impressive and the best that MPG has ever tested.
Housing the hard drive
Below, the Western Digital 18TB in OWC Mercury Elite Pro USB 3.2 enclosure — see Installing an 18TB Hard Drive into the OWC Mercury Elite Pro USB 3.2 Enclosure.