When it comes to choosing between an SSD (solid state drive) or HDD (hard disk drive) for backup storage, reliability and durability are key factors. HDDs have long been the preferred method of backup thanks to their lower costs. But with SSD prices dropping in recent years, they have become a popular alternative. SSDs have no moving parts, making them less prone to failure from shock or vibration. However, HDDs can still be a reliable backup media. This article examines the differences between SSDs and HDDs for backup in physical durability, failure rates, longevity, data recovery, cost, and performance.
What is an SSD?
An SSD, or solid-state drive, is a type of non-volatile storage device used in computers. SSDs use flash memory to store persistent data on solid state chips rather than mechanical platters like traditional hard disk drives (HDDs) (Source). The lack of moving parts allows SSDs to operate silently and have faster read/write speeds compared to HDDs.
SSDs store data on flash memory chips that retain data even when power is removed, making them non-volatile. Common types of flash memory used in SSDs include NAND flash memory and NOR flash memory. NAND is the most commonly used flash memory type for SSDs due to its higher density and lower cost compared to NOR (Source).
Overall, the solid state design of SSDs with non-volatile flash memory allows for improved performance, durability, power efficiency and reliability compared to traditional HDDs.
What is an HDD?
A hard disk drive (HDD) is a magnetic disk storage device that stores digital data. It consists of platters and read/write heads enclosed in an airtight compartment. The platters are made of a non-magnetic material and are coated with a magnetic layer. The read/write heads float over the disk surface on a cushion of air as the platters spin at high speeds, typically 5,400 rpm to 15,000 rpm.
Data is written to the platter when the write head magnetizes tiny areas of the magnetic coating in a pattern that corresponds to the data. To read the data back, the read head detects the magnetized areas as they spin under it. Older HDDs had both read and write heads, while newer drives have separate read and write heads.
HDDs were the dominant storage technology for computers until the emergence of solid state drives (SSDs). However, HDDs continue to be used in servers, data centers, desktop computers, and laptops when large storage capacity is required. They have higher storage capacities compared to SSDs and are more affordable. The downside is that HDDs have slower access times, higher failure rates, larger physical size, more noise, and higher power consumption compared to SSDs. (https://www.techtarget.com/searchstorage/definition/hard-disk-drive)
SSD vs HDD Physical Durability
SSDs are generally more durable and reliable than HDDs because SSDs have no moving parts, whereas HDDs have platters and heads that are mechanical and more fragile. The lack of moving parts is a major advantage for SSDs when it comes to physical durability.
HDDs rely on a spinning platter and a moving head to read and write data. These delicate mechanical parts are easily damaged by drops, shocks, vibrations, and extreme temperatures. The platters and heads in HDDs are sealed, but physical damage can still cause them to stop working properly.
In contrast, SSDs store data on flash memory chips. Without any moving parts, SSDs can better withstand accidental drops, shocks, vibrations, and temperature extremes. For portable external drives or devices in challenging environments, SSDs are less likely to fail due to physical damage.
According to research on Quora, dropping an SSD or HDD from over 3 meters can damage either, but the SSD is more likely to survive due to its lack of fragile mechanical parts.
SSD vs HDD Failure Rates
Research from Backblaze analyzed failure rates for over 100,000 SSDs and HDDs in their data centers over 4 years. They found that SSDs had an annualized failure rate of 1% or less through the first 4 years, while HDDs had a failure rate of 1.5-2% per year over the same period.
This translates to SSDs having a 50% lower annual failure rate compared to HDDs during this study. The significantly lower failure rates for SSDs highlight their improved reliability over traditional hard drives.
Other analyses have found similar results. A large scale study by CMU 1 of SSD and HDD failure rates in data centers reported an annual failure rate of 1-2% for SSDs compared to 3-9% for HDDs.
The superior physical durability of SSDs with no moving parts accounts for much of their improved reliability over mechanical HDDs. For important data backups where minimal risk of failure is critical, SSDs are a safer choice vs HDDs.
SSD vs HDD Longevity
SSDs have a limited number of write cycles due to the way data is stored on NAND flash memory, but modern SSDs have very high endurance ratings before they will wear out (typically multiple petabytes written). For example, the Samsung 970 EVO is rated for up to 600 terabytes written under a 5-year warranty. In contrast, HDDs do not have a limit on writes but have moving parts that fail over time.
Both SSDs and HDDs typically last around 3-5 years on average before failure. According to a Backblaze study tracking tens of thousands of drives, about 2% of HDDs fail annually, meaning they last around 5 years on average before failure. Similarly, SSDs tend to last around 4 years on average before degradation or write cycles wear them out.
While limited writes affect longevity, SSDs tend to outlast a typical use period. For most general computing uses, longevity between SSDs and HDDs is comparable in a 3-5 year period. However, SSDs are better suited for laptops due to better shock resistance.
SSD vs HDD Data Recovery
Data recovery on SSDs tends to be more complex and difficult compared to HDDs. This is because of how data is stored and managed on SSDs. SSDs spread data across multiple NAND flash memory chips with wear leveling algorithms to increase lifespan. But this makes recovering deleted files more difficult as data becomes fragmented across the drive over time (https://www.stellarinfo.co.in/blog/what-makes-ssd-data-recovery-complex/).
SSDs lack the physical moving parts of HDDs, making physical data recovery methods used for HDDs ineffective. Advanced data recovery software is required to reconstruct files spread across SSD chips. Overall success rates for SSD data recovery are lower than HDDs, with estimates around 50-70% file recovery compared to 80-90% for HDDs (https://www.acronis.com/en-us/blog/posts/are-ssds-same-league-hdds-when-it-comes-data-recovery/).
However, SSDs are less prone to physical failure that can make HDD data recovery impossible. As long as the SSD controller is functioning, data reconstruction from NAND chips remains possible in most cases. But SSD data recovery requires expertise and is costlier than HDD recovery.
SSD vs HDD Cost
SSDs are more expensive than HDDs in terms of dollar per gigabyte. Per gigabyte, SSDs generally cost around $0.20, while HDDs cost between $0.03-$0.06 per gigabyte, according to ZDNet. However, SSD costs per gigabyte have been dropping over time while HDD costs per gigabyte have remained relatively flat.
For example, a 128GB SSD cost around $625 per terabyte in 2013, according to analysis on Reddit. In 2022, a 1TB SSD from a major brand costs around $100, or $0.10 per gigabyte. Meanwhile, HDD costs have stayed between $0.03-$0.06 per gigabyte over the past decade.
So while SSDs have a higher initial price, the cost difference is narrowing over time. And for some users, the performance and durability benefits of SSDs outweigh the higher cost per gigabyte.
SSD vs HDD Performance
SSDs have much faster read and write speeds compared to HDDs. According to Tekie, an SSD can deliver read/write speeds nearly 5x that of an HDD, with NVMe drives being even faster with over 10x the write speed of an HDD [1]. Pure Storage notes that a standard HDD will read and write at typically 80-160MB/s, but an SSD can reach 200-550MB/s – over 3x as fast [2]. The Enterprise Storage Forum explains that the biggest limits to HDD speed are seek times – the delay as the read/write head moves to locate data. SSDs have no moving parts so they don’t suffer from this limitation, allowing much faster access [3]. Overall, SSDs provide a major performance advantage over HDDs when it comes to data access and transfer speeds.
[1] https://tekie.com/blog/hardware/ssd-vs-hdd-speed-lifespan-and-reliability/
[2] https://blog.purestorage.com/purely-informational/ssd-vs-hdd-speeds-whats-the-difference/
[3] https://www.enterprisestorageforum.com/hardware/ssd-vs-hdd-speed/
Conclusion
In reviewing the differences between SSDs and HDDs for backup storage, SSDs emerge as the more reliable option for most use cases. SSDs have a higher tolerance for physical shocks and vibration thanks to their lack of moving parts. Research shows SSDs have lower annualized failure rates, around 1-2% versus 3-5% for HDDs. SSDs also have longer lifespans, capable of withstanding hundreds of terabytes written over time versus only dozens for HDDs.
While HDDs have historically had a cost advantage, SSD prices continue to fall. For personal backups of irreplaceable data, the extra cost of an SSD is worthwhile for the added peace of mind. With fewer mechanical failures, SSDs provide more consistent and dependable access to backed up data when you need it most. Though HDDs still play a role in cold storage and certain enterprise applications, SSDs are the smart choice for regular access backup storage for personal and business users.