When it comes to storage, two of the main options are hard disk drives (HDDs) and solid state drives (SSDs). Both have advantages and disadvantages that make them suitable for different use cases. So which one is better, HDD or SSD?
Quick Answers
Here are some quick answers to common questions about HDDs vs SSDs:
- SSDs are faster for most real-world workloads because they have no moving parts and very low access times.
- HDDs have much higher storage capacities available per dollar compared to SSDs.
- SSDs use less power, generate less heat, and produce no noise since they have no moving parts.
- HDDs can better withstand long periods of inactivity like cold storage archives.
- SSDs have no seek time allowing faster access to randomized data.
What is an HDD?
A hard disk drive (HDD) is a traditional storage device that uses magnetic recording to store and retrieve digital data. It contains one or more rotating platters coated with magnetic material. A read/write head floats just above each platter and moves back and forth across the surface as the platters spin.
Data is written to the platter by applying a magnetic charge, and it’s read back by detecting its magnetic orientation. HDDs have been the dominant form of everyday computer storage for decades due to their cost-effectiveness and high capacity.
Advantages of HDDs
- Very high capacities – HDD capacities range from a few gigabytes up to around 16 terabytes for consumer models. Enterprise HDDs can be 10TB or higher.
- Low cost per GB – HDDs offer more capacity for your dollar compared to SSDs. As of 2019, HDD cost about $0.03 per gigabyte versus $0.20 for SSDs.
- Established technology – HDDs have over 60 years of development behind them and are a mature, well-understood technology.
Disadvantages of HDDs
- Slower random access – HDDs can only read/write sequentially and have long seek times for random access.
- More prone to failures – The mechanical nature of HDDs leads to higher failure rates than solid state drives.
- Large footprint – 3.5″ desktop HDDs require a lot of space and external power, while 2.5″ notebook drives are more physica
What is an SSD?
A solid state drive (SSD) is a storage device that uses flash memory chips to store persistent data. Unlike a hard disk, an SSD has no moving mechanical components. This enables fast read and write speeds, on the order of 100-1000x faster than HDDs for random access.
SSDs entered the consumer PC market in 2007. Adoption was initially slow due to the very high per-gigabyte cost. But as manufacturing has improved, prices have dramatically lowered and SSDs have grown in popularity for both general computing and high performance workloads.
Advantages of SSDs
- Faster access times – No seek time and very low latency provides extremely fast random access.
- Higher IOPS – SSDs can easily sustain many thousands of I/O operations per second, while HDDs are limited to 100-200 IOPS.
- Shock and vibration resistant – No moving parts makes SSDs more hardy if dropped or in high vibration environments.
- Totally silent – SSDs require no fan and are soundless since they have no moving parts.
Disadvantages of SSDs
- Lower capacities – Consumer SSD unit capacities typically top out at 4TB. HDDs go much higher.
- Higher cost per gigabyte – Though dropping, SSD $/GB is ~5-10x more than HDD technology.
- Drive writes per day – All SSDs have a limited lifespan and continuous writing will wear them out.
- File system dependence – Performance and wear levelling depends on the SSD controller and host OS file system.
Comparing HDD and SSD Performance
The primary measure of storage performance is IOPS, or input/output operations per second. This represents how many read and write operations to the drive can take place in a second. For HDDs, IOPS are typically under 200. For SSDs, IOPS can exceed 100,000.
This IOPS gap is largely driven by differences in access time. HDD access times range from 2-10 milliseconds on average for reads and writes. SSDs access times are in the microseconds, around 100x faster. This speed advantage is most pronounced when accessing random locations on the disk.
HDD vs SSD Performance Hard Disk Drive Solid State Drive Sequential Read Speed 150 MB/s 550 MB/s Sequential Write Speed 150 MB/s 520 MB/s Random Read Speed 2 ms seek + 150 MB/s 0.1 ms seek + 550 MB/s Random Write Speed 2 ms seek + 150 MB/s 0.1 ms seek + 170 MB/s Average IOPS 100-200 10,000 to 100,000 This performance difference is why SSDs can boot an operating system and launch applications much faster than HDDs. The minimal latency also benefits the system during multitasking and intensive workloads.
Comparing HDD and SSD Reliability
SSDs have no moving parts and so are less susceptible to physical damage. Typical SSD annual failure rates under normal use are around 0.5-2%, with worst-case up to 5% for low-end TLC drives. HDDs have annual failure rates of around 4%, with high-performance enterprise models up to 8-10%.
However, SSDs have a limited number of program/erase cycles due to the nature of the NAND flash technology. The cells electronically wear out with repeated writing and must be periodically refreshed. SSDs use controllers to manage this wear levelling and use over-provisioning of extra cells, but the drive will eventually wear out after enough writes.
Typical SSD life expectancy is 5-10 years for moderate consumer workloads. Heavy write usage decreases this, while cold storage increases it. HDDs can retain data integrity and be operational after 10-20 years if stored properly.
When to choose an HDD over SSD
There are some cases where HDDs are still preferred over SSDs:
- Very high capacity requirements – If you need more than 10TB of storage, HDDs are the only option.
- Archival storage – The long life and lower cost of HDDs makes them good for infrequently accessed storage.
- Frequently re-written data – HDDs support virtually unlimited writes in the same location.
- Cheap bulk storage – If you need multiples of 10TB for data that sees infrequent access, HDDs have a lower $/GB.
When to choose an SSD over HDD
SSDs outperform HDDs significantly in the following scenarios:
- OS drive or primary applications – Faster boot, launch, and response times.
- Frequently accessed games – Quicker load times. Games with faster visuals or physics benefit too.
- Disk read/write intensive work – Data analysis, engineering, content creation apps.
- Mission critical uptime – Higher reliability improves uptime with less risk of failure.
- Notebook/tablet PCs – Improves portability due to the lower weight, smaller size.
Best Uses for HDD and SSD Combination
A popular setup is to use a smaller SSD as the primary drive for OS, apps, and frequently used files paired with a larger HDD for bulk storage. This combines the speed of an SSD with the capacity of HDDs.
The SSD would contain the operating system and all applications. Programs launch faster, the system boots quicker, and fast wake from sleep is ensured. A 127GB or 250GB SSD is enough for the OS and apps for most users.
The HDD handles files like documents, photos, videos, music, downloads, etc. HD video and games are large so they also go on the HDD. A 1-4TB HDD offers ample storage for the average user. Files you are actively editing or playing can be temporarily moved to the SSD for quicker access.
SSD and HDD Performance Upgrades
For HDD-based systems, check if a 7200 RPM or even 10,000 RPM mechanical hard drive will offer performance gains. The higher speed HDDs have faster response times and bandwidth versus 5400 RPM models.
For SSD-based systems, upgrading to a higher capacity SATA SSD, a faster M.2 NVMe SSD, or adding an additional SSD will improve response across more applications, games, and files. An external SSD over USB 3.0 also typically offers better performance than traditional hard drives.
Ideal Storage Setup Examples
Here are some example best practice setups for different computers to give you ideas for your system:
Gaming PC
- 250GB SSD for Windows, apps, and 1-2 games
- 2TB 7200 RPM HDD for other games and user files
Business Notebook
- 500GB M.2 NVMe SSD as the boot drive with Windows and apps
- Optional 1-2TB 2.5″ 5400 RPM HDD for data
Home Desktop
- 500GB SSD for OS, apps, and active projects
- 3TB HDD for user files like photos, videos, music, etc.
Workstation PC
- 1TB M.2 NVMe SSD for Windows, apps, scratch disk
- 6TB RAID 10 array of enterprise HDDs for active projects
- 20TB HDD array for archival storage
Conclusion
SSDs provide a significant speed advantage for most real-world workloads compared to HDDs. However, HDDs continue to offer higher capacities at a lower price point. The ideal scenario is to utilize both in a computer system.
Use a fast SSD as the primary drive for OS, apps, games, and active files where speed matters. Supplementary HDDs provide mass storage for user files that are accessed less frequently. With this combo, you get the responsiveness of an SSD and the huge capacity of spinning hard drives.
