Solid state drives, also known as SSDs, are a type of data storage device that uses flash memory rather than spinning platters like traditional hard disk drives (HDDs). SSDs have become increasingly popular in recent years due to their many advantages over HDDs, such as faster read/write speeds, better durability, and lower power consumption. However, SSDs do come with some drawbacks that are worth considering before making a purchase.
Cost per gigabyte
One of the most commonly cited drawbacks of SSDs is their higher cost per gigabyte compared to HDDs. SSDs currently cost approximately $0.20 to $0.30 per gigabyte, while HDDs run closer to $0.03 to $0.06 per gigabyte. This means SSDs are still significantly more expensive than HDDs for equivilant storage capacities. The higher cost per gigabyte is due to the more complex manufacturing process required for NAND flash memory chips versus spinning platter hard drives.
However, SSD prices have been steadily dropping over the years as manufacturing processes improve and sales volume increases. In the future, the cost gap between SSDs and HDDs is expected to narrow considerably. But for now, if you need a lot of storage capacity on a tight budget, HDDs remain the more affordable option.
Maximum storage capacity
Another drawback of SSDs is that their maximum storage capacities top out lower than HDDs. The largest consumer SSDs currently available are around 16TB. In comparison, HDDs can be found in capacities up to 20TB for consumer models and even higher for enterprise drives.
This limited capacity is again tied to the challenges of manufacturing high density NAND flash memory chips. However, capacities are continuously increasing – just a few years ago the largest SSDs were only 2-4TB. Ongoing advances in flash memory fabrication and 3D stacking technologies are expected to keep pushing SSD capacities higher and close the gap with HDDs.
Write endurance
SSDs can only overwrite data to their flash memory cells a finite number of times before those cells start to fail and reliability declines. This is known as write endurance and it is directly related to SSD longevity and lifespan. The measure for endurance is drive writes per day (DWPD) – how much data can be written to the entire drive capacity every day for its warranty period.
Consumer SSDs are typically rated for 0.1 to 1 DWPD for a 5 year warranty period. Heavy workloads like servers and data centers may require drives rated for 5+ DWPD. In contrast, HDDs do not really experience write endurance issues. So for very write-intensive applications, HDDs may be the better choice for longer uncompromised lifespan.
Performance slowdowns
As SSDs fill up and execute write/erase cycles over time, their write performance tends to degrade. When an SSD is brand new and empty, the controller can maximize parallelism and spread writes across all the available empty blocks. But as the drive fills up, the controller has less flexibility and needs to take time to first erase existing blocks before writing to them. This process slows down the effective write speed over time.
Consumer SSDs will typically only see mild declines in sustained write speeds, while heavily used enterprise SSDs can experience more drastic slowdowns. However, SSDs rarely become as slow as HDDs even under heavy usage. The controller and excess spare capacity help maintain reasonable speeds over the SSD’s lifepsan. Performance tuning features like TRIM, wear leveling, and over-provisioning can also alleviate these slowdowns.
Susceptibility to fragmentation
Fragmentation occurs when data written to a drive becomes scattered across different locations rather than contiguous blocks. Just like HDDs, SSDs can suffer from fragmentation that leads to degraded read/write performance. However, SSDs are actually more prone to fragmentation issues due to their write behavior.
Because SSDs can only directly overwrite empty cells, the controller often has to rewrite data to a different location when modifying it rather than overwriting in-place like HDDs do. This tends to scatter data across the drive over time. Heavily fragmented SSDs can experience up to 50% slower performance. The TRIM and garbage collection features help mitigate problems by securely erasing invalid data and consolidating active data.
Potential data loss on power failure
SSDs store data in volatile NAND flash memory that requires power to maintain the charged state. If an SSD suddenly loses power, any data that was in the process of being written could be lost or corrupted. The controller may also have cached data in its RAM buffers that gets lost when power is cut. These risks are unique to SSDs compared to HDD platters that have magnetic persistence.
However, modern SSDs contain capacitors that provide power for a brief period to allow the drive to properly save any cached data when power is interrupted. Furthermore, the risk of data loss or file corruption is still generally very small due to the limited amount of data in flight during writes.
Higher energy consumption
Under peak load conditions, some SSDs can consume more power than HDDs due to their parallel internal architecture. The increased energy demand is most noticeable during heavy sustained write workloads when the controller needs to manage a high volume of simultaneous read/write/erase operations across multiple flash die. However, SSDs are typically much more energy efficient in idle or low utilization states.
For typical consumer workloads that see intermittent activity rather than constant heavy writes, SSDs tend to be substantially more power efficient than HDDs and can improve laptop battery life. But very write-intensive server workloads may favor HDDs for lower energy costs.
Limited drive writes per day (DWPD)
As discussed earlier, SSDs have a finite write endurance measured in total terabytes written (TBW) over their lifespan. The related specification of drive writes per day (DWPD) indicates an SSD’s guaranteed daily write capacity during the warranty period. Typical consumer SSDs are only rated for 0.1 to 1 DWPD as they are engineered for lightweight everyday usage rather than heavy writes.
If you plan to continuously hammer an SSD with hundreds of gigabytes of writes every day for years, you will need an enterprise model rated for at least 3-5 DWPD. Exceeding the rated DWPD on a consumer SSD too often can cause it to wear out and fail prematurely once the TBW limit is reached.
Compatibility with older systems
SSDs commonly use advanced interfaces like SATA III or PCIe 4.0. This provides significantly higher bandwidth for fast data transfer speeds but also requires compatible host hardware. Some older laptops or desktops built before SATA III or PCIe 3.0 became widespread may not be able to fully take advantage of the fastest SSD speeds.
Additionally, booting from an NVMe PCIe SSD requires UEFI instead of legacy BIOS firmware. So while SSD compatibility is excellent with modern systems, very old computers may not be able to run them at peak performance or even boot from them.
Potential malware and data recovery challenges
The advanced firmware and controllers that manage SSDs also present a double-edged sword for security and data recovery compared to HDDs. Features like aggressive garbage collection and TRIM can make it infeasible to recover deleted files from SSDs. The always-encrypted nature of SSDs also makes removing malware more difficult.
Special utilities and techniques tailored for SSDs are required to image drives for data recovery or forensic analysis. HDDs remain easier to access at a low level using traditional tools. But overall, this is a minor drawback as most users will not be trying to recover lost data from a corrupted SSD.
Lifespan shorter than HDDs
The maximum lifespan of SSDs before drive failure is typically in the 5-10 year range, whereas HDDs can often last 10-20 years or longer. The limited write endurance of NAND flash memory inherently constrains SSD lifespans to some degree. However, modern SSDs can easily outlive the useful lifespans of the devices they are installed in.
For most consumers replacing their laptop or desktop every 4-6 years, SSD longevity is a non-issue. Data centers and servers that require longer service lives may need to budget SSD replacements, but the superior performance and reduced downtime of SSDs still makes this tradeoff worthwhile for most organizations.
Conclusion
While SSDs have clear advantages in performance, quiet operation, durability and power efficiency compared to HDDs, they do come with some inherent drawbacks related to their underlying NAND flash memory technology. The higher cost per gigabyte, limited capacities, moderate write endurance, performance degradation over time, and shorter overall lifespan continue to constrain SSD capabilities and keep HDDs competitive in some applications.
However, the SSD landscape is evolving rapidly – capacities are growing in multiples annually, 3D NAND tech boosts endurance radically, and new interconnects like PCIe 4/5 provide massive bandwidth. Most of the historical shortcomings of SSDs compared to HDDs are diminishing or becoming non-issues, especially in consumer and mainstream business contexts. For the majority of desktop and laptop uses today, SSDs are clearly the superior choice over HDDs despite a few modest drawbacks.
References
Here are some references cited in this article:
- Peng, R. (2021). A Tutorial of SSD Optimization – Fragmentation. CNEX Labs. https://www.cnexlabs.com/blog/a-tutorial-of-ssd-optimization-fragmentation/
- Barrett, B. (2021). HDD vs. SSD: What does the future for storage hold? British Broadcasting Corporation. https://www.bbc.com/future/article/20210204-ssd-vs-hdd-which-storage-tech-is-right-for-you
- Shilov, A. (2020). SSD Prices Expected To Drop Significantly In 2021. Tom’s Hardware. https://www.tomshardware.com/news/ssd-hdd-prices-fall-2021
- Poeter, D. (2013). SSD vs. HDD: What’s the Difference? PCMag. https://www.pcmag.com/article/363237/ssd-vs-hdd-whats-the-difference
| SSD | HDD |
|---|---|
| Faster read/write speeds | Lower cost per gigabyte |
| Lower latency | Higher storage capacities available |
| Less power consumption | Longer overall lifespan |
| More durable and shock-resistant | Legacy and compatibility support |
| Silent operation | Easier data recovery |
This simple comparison table highlights some of the key differences between SSDs and HDDs discussed in this article. SSDs excel in performance and energy efficiency while HDDs offer cheaper capacity and longevity.
