Exos X20 20TB vs HC550 18TB
The Exos X20 20TB and the HC550 18TB are both enterprise hard drives we supply tested from Hong Kong, and the figures below are the same ones published on each product page. They share 2 listed specification rows and separate on recording, interface, sustained transfer, so the decision is less about "which is better" and more about which of those differences your platform or workload can actually use.
Nothing on this page is a price: used and refurbished hardware is repriced weekly, so both are quoted on request against confirmed stock with the date the quote holds until. If you are replacing a part, send the platform and we will confirm the population before you commit.
Side by side
Exos X20 20TB vs HC550 18TB specifications
| Specification | Exos X20 20TB | HC550 18TB |
|---|---|---|
| Recording | CMR, 7200 rpm, 256MB cache | CMR (energy-assisted PMR), 7200 rpm, 512MB cache |
| Interface | SATA 6Gb/s, 512e (4Kn and SAS 12Gb/s variants exist) | SATA 6Gb/s, 512e (SAS 12Gb/s variant: WUH721818AL5204) |
| Sustained Transfer | Up to 285 MB/s | Up to 269 MB/s |
| Form Factor | 3.5-inch, 10-platter helium-sealed | 3.5-inch, 9-disk HelioSeal |
| Workload Rating | 550 TB/year | 550 TB/year |
| Reliability | 2.5M hours MTBF, 5-year class | 2.5M hours MTBF, 5-year class |
| Power / Security | PowerBalance, Seagate Secure (ISE/SED options) | not stated |
| Model | Seagate Exos X20 20TB (ST20000NM002H, SATA) | WD Ultrastar DC HC550 18TB (WUH721818ALE6L4 / 0F38459) |
| Security | not stated | Instant Secure Erase; SED options in the family |
Rows that differ are highlighted. Figures are the same ones published on each product page; where a figure is community-sourced rather than vendor-published it is stated on that page. Confirm every part against your build sheet when ordering.
Where they differ
- ·Recording — Exos X20 20TB: CMR, 7200 rpm, 256MB cache; HC550 18TB: CMR (energy-assisted PMR), 7200 rpm, 512MB cache.
- ·Interface — Exos X20 20TB: SATA 6Gb/s, 512e (4Kn and SAS 12Gb/s variants exist); HC550 18TB: SATA 6Gb/s, 512e (SAS 12Gb/s variant: WUH721818AL5204).
- ·Exos X20 20TB is the better figure for sustained transfer rate (Up to 285 MB/s vs Up to 269 MB/s).
- ·Form Factor — Exos X20 20TB: 3.5-inch, 10-platter helium-sealed; HC550 18TB: 3.5-inch, 9-disk HelioSeal.
What they share
Workload Rating: 550 TB/year; Reliability: 2.5M hours MTBF, 5-year class.
Decision
Which one to buy
Hard drives are a density decision. Capacity per drive sets how many spindles — and therefore how much rack, power and cooling — a given usable capacity costs, and sustained transfer sets how long rebuilds and backups take. For bulk storage the highest capacity per drive usually wins on total cost of ownership; for arrays that are rebuilt often, the workload rating and transfer rate matter more than the headline capacity. Both models above are CMR enterprise parts — check the interface (SATA versus SAS) against your enclosure before ordering.
Choose the Exos X20 20TB if
- ·Recording: CMR, 7200 rpm, 256MB cache
- ·Interface: SATA 6Gb/s, 512e (4Kn and SAS 12Gb/s variants exist)
- ·You need more sustained transfer rate — the Exos X20 20TB lists Up to 285 MB/s against Up to 269 MB/s on the HC550 18TB.
Choose the HC550 18TB if
- ·Recording: CMR (energy-assisted PMR), 7200 rpm, 512MB cache
- ·Interface: SATA 6Gb/s, 512e (SAS 12Gb/s variant: WUH721818AL5204)
- ·Form Factor: 3.5-inch, 9-disk HelioSeal
Photos
What the two look like
Exos X20 20TB
Photo from the Exos X20 20TB page. Every unit's label is read against your order before dispatch.
HC550 18TB
Photo from the HC550 18TB page. Every unit's label is read against your order before dispatch.
Frequently asked questions
How much do the Exos X20 20TB and the HC550 18TB cost?
We do not publish prices for either: secondary-market hardware is repriced weekly. Send the quantity, the platform and the condition you want and we quote both against confirmed stock, with the date the figure holds until.
What is the main difference between the Exos X20 20TB and the HC550 18TB?
Recording (Exos X20 20TB: CMR, 7200 rpm, 256MB cache; HC550 18TB: CMR (energy-assisted PMR), 7200 rpm, 512MB cache); Interface (Exos X20 20TB: SATA 6Gb/s, 512e (4Kn and SAS 12Gb/s variants exist); HC550 18TB: SATA 6Gb/s, 512e (SAS 12Gb/s variant: WUH721818AL5204)); Sustained Transfer (Exos X20 20TB: Up to 285 MB/s; HC550 18TB: Up to 269 MB/s).
Can I use the Exos X20 20TB and the HC550 18TB in the same system?
Yes, if the bays and interface match, and both are CMR parts. Mixed capacities are fine in most arrays, though your controller may require matched drives per RAID group.
Which one should I buy?
Buy the one whose strong points match the job: see the "Choose" section above. If you are replacing an existing part, send the platform or the old part number and we will confirm compatibility before you order.
What condition are they in, and do you ship worldwide?
Both are supplied tested with a 1-year written warranty. Condition is stated line by line before you order — new, decommissioned pull or OEM tray — and we ship worldwide from the Hong Kong warehouse with full export documentation, typically 3–7 days by air.
Get a quote for either — or both
Tell us the quantity, the platform and the condition you need. We confirm stock and put a firm figure in writing with the date it holds until.
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