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Four 22TB Hard Drives

WD Purple Pro 22TB

re: Installing an 18TB Hard Drive into the OWC Mercury Elite Pro
re: Formatting a new Hard Drive or SSD in Apple Disk Utility
re: Western Digital 18TB Ultrastar DC HC550 Hard Drive

Questions on storage, RAID, backup, reliability? Consult with MPG Lloyd.

Evaluation of four 22TB hard drives.

The WD 22TB Red Pro 7200 rpm SATA III 3.5" Internal NAS HDD WE221KFGXSPB was planned to be included, but it was dead on arrival and could not be formatted, making nothing but erratic clicking sounds.

The OWC Thunderbay 8 enclosure (about $800 for 0TB) was used to house the drive. Its Thunderbolt 3 interface offers 8 bays with 4 SATA channels. Each drive was positioned to have full SATA bandwidth (slots 1/3/5/7) all to itself.

As this was written, OWC was not selling 22TB drives. Check via these links below.

Choosing a drive capacity

Hard drives slow down as they fill up. A good way to evaluate hard drive is by its average speed across the capacity that will be used, as well as how it performs at around 80% capacity usage, plus its consistency across the capacity.

When purchasing hard drives, MPG recommends capacities that will keep actual storage used at no more than 80% of capacity, so as to maintain reasonably high speed. For example, anticipation of up to 16TB of storage needs suggests a 20TB hard drive (16TB is 80% of 20TB).

All of these drives have very similar specifications similar to the WD Purple Pro. It’s not clear to me what if any real difference there is between them.

  • 22TB Storage Capacity
  • 3.5" Form Factor
  • SATA III 6 Gb/s Interface
  • 512MB Cache
  • 7200 rpm
  • Up to 265 MB/s Sustained Data Transfers
  • 600,000 Load/Unload Cycles
  • 550TB per Year Workload Rating
  • Designed for 24/7 Surveillance
  • Supports up to 64 HD Cameras

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.

Use the fill-volume command of diglloydTools DiskTester to determine performance across drive capacity for hard drives or SSDs, single drives or RAID of any kind.

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.

Test results: Speed across 22TB capacity

Test mule was the 2019 iMac 5K with the OWC Thunderbay 8 enclosure.

The fill-volume command of diglloydTools Disktester was used, with 128MB transfer size.

For over 13 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 more consistent ones. But here, only a single drive was available for testing.

MiB = 1024 * 1024, multiply by (1024/1000)^2 = 1.048 for MB/sec.

All of these drives deliver essentially the same performance, but best overall by a teeny bit is the Seagate Iron Wolf Pro.

  • On the fastest part of the volume, speed is very fast for a hard drive, around 275 MiB/sec.
  • At 50% capacity speed is down to about 230 MiB/sec—still very fast for a hard drive.
  • At 80%, about 180MiB/sec—not bad, since that is at ~18TB of capacity usage.
  • Past 80% capacity, speed drops off abruptly to marginal.
  • At the 18TB mark, substantially faster than 18TB hard drives (~150 vs ~127 MiB/sec).

Hard drives slow down as they fill up. For the goal (for example) of 200 MiB/sec minimum speed, then a 22TB drive delivers it for about the first ~15GB of capacity (partitioning the drive can guarantee that the fastest portion is used).

Average Write speed:  222 MiB/sec = 233 MB/sec
Average Read speed:   224 MiB/sec = 235 MB/sec

Vertical scale is MB/sec. Horizontal scale is percentage of volume capacity eg 50% of 20TB volume is 10TB.

22TB hard drives: speed across 22TB volume capacity

Test results: speed vs transfer size

Test mule was the 2019 iMac 5K with the OWC Thunderbay 8 enclosure.

The run-sequential-suite command of diglloydTools Disktester was used for this data.
disktester run-sequential-suite

Transfer performance for 32K and 64K transfers is outstanding for all the drives except the WD Purple Pro, which takes 256 KiB transfers before achieving full speed.

Best overall is the Seagate Iron Wolf Pro.

22TB hard drives: speed vs transfer size


Questions on storage, RAID, backup, reliability? Consult with MPG Lloyd.

Other factors not considered in this testing include other workloads, power consumption, failure rate over time, RAID performance, etc. The differences are not likely to amount to much.

Assessed as hard drives, these are all very fine performers—state of the art.

The purpose of such drives is for ultra high capacity storage—overflow storage and/or backup, at a reasonable cost per terabyte. For that, all of these drives deliver the goods in an indistinguishable way.

However, compared to a fast USB4 SSD like the OWC Express 1M2, all of these drives are slow as molasses—about 5% of the speed (20X slower!).

As this was written, OWC was not selling 22TB drives. Check via these links below.

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