Comparing SSD vs HDD Speed: Which Is Faster?

Solid-state drives (SSDs) have become a popular storage choice for enterprises because of their high speeds compared to hard disk drives (HDDs). A SATA-interface SSD is often double the read/write speed of a SATA HDD, and some NVMe SSDs have 10 times the read and write rates of HDDs.

But hard drives are still part of the market: although hard drive shipments are decreasing overall, according to Horizon Technology, major hard drive manufacturers are still producing drives designed for enterprise storage use cases. And even though SSD prices continue to decrease overall, hard drives are still cheaper and offer cost-saving benefits to some enterprises. This piece analyzes the differences between SSDs and HDDs and which storage use cases they’re most suited to, including rapid data processing and archive storage.

SSD vs. HDD speeds

Comparison of SSD and HDD speeds

The following table shows manufacturer-provided data on sample solid-state drive and hard drive speeds. Note that sustained transfer rate, or sustained data rate, is a common term that hard drive manufacturers use for the process of reading and writing data on a disk. SSD manufacturers phrase the speed differently.

Drive Type Drive Model Speed
Hard drive speeds Toshiba MG Series with SATA interface, model MG06ACA800E, 8 TB capacity Up to 241 MB/s, sustained transfer rate
Seagate EXOS 2X18 with SATA or SAS interface, 18 TB capacity Up to 554 MB/s, sustained data rate
Solid state drive speeds Micron 5200 ECO with SATA interface, 7.68 TB capacity 540/520 MB/s, sequential read/write speeds
Western Digital PC SN720 with NVMe interface, 1 TB capacity 3,400/2,800 MB/s, sequential read/write speeds

SSD vs. HDD read/write speeds

How much faster is an SSD? This depends on both the hard drive and the solid-state drive. NVMe SSDs can exceed even SATA SSD speeds by up to 10 times. And although hard drives are significantly slower overall, some hard drives can still meet enterprise use cases. Vendors like Seagate are still manufacturing scalable, high-performance HDDs, after all. To determine what your storage infrastructure needs, study the breakdown of hard drive and solid-state drive specifications.

Learn more about NVMe SSD rates.

SSD read/write speed

Historically, SSDs have been designed to be drop-in replacements for HDDs, which means they’re often made with the same interfaces as HDDs. In practice, this means a SATA interface or on more high-performance systems a SAS interface.

These interfaces have been optimized specifically for HDD storage devices, but they are suboptimal for SSDs. “Interfaces do get in the way for SSDs,” said Jim Handy, an analyst at Objective Analysis, “and that’s why we are seeing PCIe SSDs.” PCIe SSD interfaces are designed to better suit solid-state technology, enabling higher flash speeds.

To get an idea of the benefit of a more SSD-friendly interface, like PCIe, consider this. The SATA 3.0 specification only allows SSDs to reach a maximum data rate of about 560 MB/s. By contrast, the PCIe 3.0 interface allows speeds of 985 MB/s per lane. And PCIe Gen 4 permits 16 gigatransfers per second (GT/s) for each PCIe lane, about 2 gigabytes per second, according to Kingston Technology.

The SSD’s controller is connected by multiple lanes to different NAND chips where the data is actually stored. Even though an individual NAND chip is unlikely to be able to work at a 985 MB/s, a device with eight chips on separate lanes can easily offer 3,000 MB/s aggregate throughput.

Learn more about the differences between NVMe and SATA drives.

How to improve SSD speed

Another way that SSD speed can be increased is to use faster NAND. Standard NAND used in SSDs is effectively flat, and performance-sapping error correction algorithms are used to mitigate against data corruption caused by cell to cell interference in closely packed cells. But new flash chip technology uses multiple layers of memory cells, known as 3D NAND, and this offers the potential for faster SSD read and write performance. That’s because it’s not necessary to run these algorithms in 3D NAND, and chipmaker Samsung has said its 3D NAND is twice as fast as conventional planar NAND when it comes to SSD write speed.

HDD read/write speed

The biggest limits to HDD speed are seek times, the delay as the read/write head moves into position, and latency, as the hard drive waits for the required part of the disk to rotate into position under the head.

How to improve HDD speed

Reducing seek times to increase HDD performance is possible. It’s commonly achieved using a trick called “short stroking.” This involves using only a portion of an HDD’s capacity, for example by only using the outermost 10% of each platter. By doing this, the read/write head only has to cover a distance one-tenth as far as if the whole platter was in use, and on average, it will be far closer to where it needs to move to for each read or write operation.

Although there will be a significant increase in hard drive speed, the downside to short stroking is its inefficiency. Only a small portion of the HDD storage capacity can be utilized even though the power consumption remains unchanged.

Reducing latency is also relatively simple: increasing the rotation rate of the platters will reduce latency, and for that reason, some high-performance HDDs rotate at 15,000 rpm rather than the more standard 7,200 rpm.

Rotating the platters faster than 15,000 would result in further reductions in latency, but for practical reasons, this is difficult to achieve: the faster the platters spin, the less stable they are. Faster spinning disks also consume far more power. Both of these issues have been addressed in part by filling HDDs with helium, but for the moment, 15,000 rpm appears to be the limit.

How to measure drive speeds

Performing read/write tests, using tools like benchmarking software, helps gauge the best possible performance of a hard drive or SSD. These tools test overall raw speed, internet connection speed, and RPM.

Also keep in mind that the speeds given for drives are usually their peak performance; actual speeds may be lower. The rates given by storage providers often capture speeds in ideal laboratory conditions.

Drives also need regular health checks; these can reveal problematic spots on the drive that contribute to speed. If IT and storage teams are able to identify these problems and fix them, they’ll have a better chance of improving their drive performance and longevity.

Benchmarking SSD and HDD speeds

SSDs and HDDs are usually supplied with manufacturers’ specifications, but to get the most accurate speed comparison between an SSD and HDD, you’ll need to run a performance benchmark exercise using benchmarking software.

These solutions are designed to measure transfer speeds under different conditions, such as sequential reads and writes, where all the data is in the same area, and random reads and writes, to different parts of the storage medium.

Popular drive performance benchmark software includes:

  • CrystalDiskMark: This is a popular and easy-to-use tool that carries out both SSD and HDD benchmarking.
  • Atto Disk Benchmark: This is a widely accepted tool that can benchmark SSDs and HHDs as well as RAID arrays and host connection to attached storage.

Read more about hard drive benchmarking tools.

Who should use SSDs and HDDs?

Enterprises’ different storage needs will determine which drives they should use. Most businesses with a large storage infrastructure will have both SSDs and hard drives, but the environments in which they’re deployed depend on cost effectiveness and data processing needs.

When to use SSDs

Although they’re priced higher than hard drives, SSDs are typically worth the investment for enterprises with rapid data access requirements. High-performance business applications and critical data processing workloads are a couple examples that necessitate SSD speeds. And just because solid-state arrays are also becoming the industry standard, it makes sense to include them in your company’s storage infrastructure, even if you have hard drives too.

When to use HDDs

Hard drives are ideal for infrequently accessed data, especially if enterprises need to archive large volumes. Massive amounts of data require significant storage capacity, and large HDD capacity is cheaper. Save SSDs for rapid access use cases and maximize the less expensive hard drives for your long-term storage libraries.

Bottom line: SSD vs. HDD speed

Solid-state drives are faster than hard drives overall, and they’re more suitable for high-performance workloads and rapid data processing needs. Enterprises with major applications that require a great deal of processing power should have SSD arrays in their data centers or offices. But hard drives are beneficial too; they’re less expensive, and they’re good choices for long-term storage. Archiving data on hard drives offline can also protect that information from ransomware.

And yes, SSDs have become much more affordable over the years, so businesses that couldn’t originally afford them might now shift their attention to flash memory. But this doesn’t yet negate the importance of hard drives: they’re still used in many systems, and though they don’t have the speeds of SSDs, they’re still a valid choice for long-term storage and for businesses that keep their hard drives healthy.

Paul Rubens
Paul Rubens
Paul Rubens is a technology journalist based in England and is an eSecurity Planet and Datamation contributor.
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