Read on 2026-10-16. The source is a post from a cloud backup company that runs a very large drive fleet. This page reports what it says. It does not test drives and does not rank products.
How an HDD stores data
Backblaze, in its post “Hard Disk Drive (HDD) vs. Solid-state Drive (SSD): What's the Diff?”, says that a hard drive has a platter, or stacked platters, which spin around a central axis (a spindle), typically at about 5,400 to 7,200 revolutions per minute. It adds that information is written to and read from the drive by changing the magnetic fields on those spinning platters using an armature called a read-write head. It also says that the two most common form factors for hard drives are 2.5 inch, common for laptops, and 3.5 inch, common for desktop machines. The same post says that the vast majority of drives in use today connect through a standard interface called Serial ATA (or SATA).
How an SSD stores data
The same post says that solid state is industry shorthand for an integrated circuit, and that is the key difference between an SSD and a HDD: there are no moving parts inside an SSD. It adds that rather than using disks, motors and read-write heads, SSDs use flash memory instead, that is, computer chips that retain their information even when the power is turned off. It also says that many SSD makers produce SSD mechanisms that are designed to be plug-and-play drop-in replacements for 2.5 inch and 3.5 inch hard disk drives, equipped with the same SATA interface and power connector you might find on a hard drive.
Side by side
The pros and cons chart in the same post lists these points for each drive type.
| Point | HDD | SSD |
|---|---|---|
| Cost | Budget-friendly | Can be expensive |
| Capacity | Lots of storage space | Less storage capacity than HDDs |
| Speed | Slower than SSDs | Faster than HDDs |
| Noise | Noisy | Don't generate noise |
| Power | Use a lot of power | Use less power than HDDs |
| Wear | Moving parts make them prone to wearing out over time | No moving parts make them more durable than HDDs |
Capacity and power in numbers
Backblaze, in its NAS buying guide published May 30, 2024, says that its HDD vs. SSD table has a row for capacity and a row for power consumption.
| Point | HDD | SSD |
|---|---|---|
| Capacity per drive | up to 20TB+ | typically up to 8TB |
| Power consumption | (Idle) 2–5 watts (Active) 2–6 watts | (Idle) 0.5–1 watt (Active) 2–3 watts |
Capacities move as new drives ship, so read the spec sheet of the drive you are looking at for its own figures.
Which job suits which drive
Backblaze, in its NAS buying guide, says that the high capacity per gigabyte of HDDs makes them ideal for storing large media files, backups, and infrequently accessed data. It adds that if you prioritize speed and performance for applications like video editing, databases, or frequently accessed files, SSDs are a better option. It also says that a hybrid approach lets you leverage the strengths of both technologies: HDDs for bulk storage and SSDs for performance-critical tasks.
Both kinds of drive fail
Backblaze, in its HDD vs. SSD post, says that just like hard drives, SSDs can wear out, though for different reasons. It adds that whether you're using a HDD or an SSD, a good backup plan is essential because eventually any drive will fail.
The guides on hard drive failure data and SSD endurance numbers go into how each type wears.
Before you buy: what to write down
- How much you need to store today and in a few years. The storage calculator does the sum.
- The connector in your computer or NAS: SATA, or an M.2 slot, and which kind. The NVMe vs SATA guide lists the checks.
- Whether the files are read all day (speed matters) or stored and rarely opened (capacity matters).
- Where the backup lives. A drive is not a backup of itself; see NAS or external hard drive.
Sources
Checked on 2026-10-16 against Backblaze: HDD vs. SSD, What's the Diff?, Backblaze: NAS Buying Guide. Read the source again before you rely on a number, because posts get updated and drive models change.
Related guides
- NVMe vs SATA SSD: Interface limits, M.2 and what to check before you buy, with a transfer-time calculator.
- SSD lifespan: TBW and P/E cycles: How to read endurance numbers on a spec sheet, with a write-budget calculator.
- How much storage do I need: A calculator from the source's sizing formulas, with RAID overhead.