Having a reliable backup solution is critical for protecting important data against loss from hardware failure, accidental deletion, malware, and other threats. The two main options for backup storage devices are solid state drives (SSDs) and hard disk drives (HDDs). But which one provides better reliability for backups?
SSD vs HDD – Overview
SSDs and HDDs use different technologies for storing data. SSDs utilize flash memory chips while HDDs use magnetic disks. Some key differences between the two include:
- SSDs have no moving parts, making them more resistant to physical damage.
- HDDs contain spinning magnetic disks, making them more prone to failure from shocks or drops.
- SSDs are much faster for reading and writing data due to flash memory.
- HDDs tend to be cheaper per gigabyte of storage capacity.
- SSDs wear out over time with use unlike HDDs which can last longer with proper care.
These differences impact the reliability of SSDs and HDDs for backup usage. Here is a more detailed comparison.
Durability and Lifespan
SSDs are more durable and withstand shock/impact better than HDDs. HDDs contain rapidly spinning disks and mechanical arms that are sensitive to physical bumps or drops. This makes them more prone to failure if mishandled.
SSDs have no moving parts and use flash memory chips rather than magnetic platters. They are very resistant to physical damage from drops or impacts. However, SSDs have a limited lifespan based on the number of erase/write cycles the memory cells can handle before wearing out.
| Storage Type | Durability | Expected Lifespan |
|---|---|---|
| SSD | High – no moving parts | 5-10 years typical use |
| HDD | Moderate – contains fragile moving parts | 3-5 years typical use |
For backups that experience less frequent data rewrites, SSDs can easily provide 5-10 years of usage. HDDs tend to last 3-5 years on average before mechanical failure becomes more likely. Overall, SSDs have an advantage in durability and lifespan for backup usage.
Shock and Vibration Resistance
Since they contain no moving parts, SSDs are completely immune to damage from shocks or vibration. They can withstand significant shock from drops without any performance impact or loss of data integrity.
HDDs contain sensitive internal components like spinning disks and mechanical arms that can fail when subjected to external shocks or vibration. Dropping an HDD has a high chance of causing physical damage and resulting data loss. They must be handled with care to prevent failure.
This makes SSDs much better suited for backup situations where physical impacts or drops are a risk, such as with external portable hard drives. The mechanical nature of HDDs means they should be protected against excessive shocks and vibration through mounting or padding if used for backup.
Temperature Tolerance
SSDs are able to operate in a wide temperature range typically between 0°C to 70°C. However, their performance and lifespan may decrease if run for extended periods at high temperatures above 50°C.
HDDs are sensitive to both high and low temperature extremes. Most HDDs are rated to operate between 5°C to 60°C. Exposing them to cold or hot temperatures outside this range increases the risk of failure.
| Storage Type | Operating Temp Range |
|---|---|
| SSD | 0°C to 70°C |
| HDD | 5°C to 60°C |
The wider temperature tolerance of SSDs makes them better suited for backup in environments subject to temperature swings. HDDs require monitoring of ambient temperatures to prevent early failure.
Data Integrity and Long-Term Retention
SSDs and HDDs use very different methods for storing data, which impacts long-term data retention.
HDDs store data magnetically on spinning platters inside the drive enclosure. As long as the external conditions remain within acceptable limits, the stored data can remain intact for many years with minimal deterioration.
SSDs store data in flash memory cells. These cells have a limited lifespan and may lose charge over time if left unpowered, leading to data loss. However, modern SSDs contain capacitors that provide enough backup power to allow cached data to be written to memory in the event of sudden power loss.
For archival data that will be rarely accessed, HDDs are a better choice for long-term retention measured in years. However, SSDs still offer adequate data retention for backups that are accessed more regularly and replaced every 3-5 years.
Magnetic Data Decay in HDDs
While HDDs can retain data for many years, even they are still subject to very gradual magnetic decay. As the physical magnetic charge storing bits slowly fades, data errors begin accumulating after around 10-20 years unless periodic data scrubbing is performed.
Thus for true archival data that may be seldom accessed but still needs to be retained indefinitely, storage on magnetic tape is recommended rather than HDDs. Magnetic tape is rated for 30+ year retention with minimal decay.
Power and Environmental Requirements
SSDs consume much lower power compared to HDDs. They do not need to spin up disks and move mechanical arms. This allows SSDs to operate at lower voltages as well.
| Storage Type | Power Consumption | Voltage Requirements |
|---|---|---|
| SSD | 2-4 watts typical | 3.3-12V DC |
| HDD | 6-12 watts typical | 5V or 12V DC |
The minimal power requirements make SSDs easy to integrate into embedded systems running off batteries or solar power. HDDs typically need a stronger external power source to handle peak power draws from spin-up current surges.
SSDs produce negligible noise and can operate well in acoustic sensitive environments. HDDs generate low but noticeable operating noise from spinning disks and mechanical components. Excessive external vibration can also impact HDD performance and reliability.
Available Storage Capacities
HDDs currently provide much higher maximum storage capacities compared to SSDs. The largest HDDs can store up to 20TB, while typical high capacity SSDs max out at around 8TB currently.
| Storage Type | Typical Capacity Range |
|---|---|
| SSD | 250GB – 8TB |
| HDD | 500GB – 20TB |
Very high capacity needs for backups approaching 20TB will require HDDs. However, 8TB SSDs can still adequately serve most small business backup requirements.
Cost Per Gigabyte
HDDs continue to provide a much lower cost per gigabyte compared to SSDs. Typical HDD cost is around $0.02 – $0.03 per gigabyte depending on speed and form factor. SSD cost ranges from $0.10 to $0.15 per gigabyte for SATA models up to $0.20+ for high performance NVMe SSDs.
The maximum capacities of HDDs also mean the total storage amount in a backup server or NAS can be maximized while staying within budget constraints. However, SSD prices continue to fall making them more affordable for backups.
Transfer Speed
SSDs provide tremendously faster data transfer speeds compared to HDDs due to flash memory and the lack of moving parts. This makes backups and restores much quicker.
| Storage Type | Interface | Typical Sustained Speed |
|---|---|---|
| SSD | SATA | 500+ MB/s |
| HDD | SATA | 100-200 MB/s |
| SSD | NVMe | 3000+ MB/s |
| HDD | SAS | 200-400 MB/s |
For large volume backups, the slower speeds of HDDs increase the time required to complete the operation. With SSDs, backups can finish much quicker.
Impact of Fragmentation
File fragmentation on HDDs causes backup speeds to progressively slow down as more fragmented data is copied. SSDs maintain high speeds regardless of fragmentation levels.
Failure Rate and Reliability
SSDs have lower annualized failure rates (AFR) compared to HDDs when used appropriately within their design limits for temperatures and wear. Typical AFR figures are:
| Storage Type | Annualized Failure Rate |
|---|---|
| SSD | 0.2% – 0.5% |
| HDD | 2% – 4% |
These numbers represent a broad average across drive models and usage conditions. But they indicate SSDs can provide around 4-5X greater reliability and lower failure risk compared to HDDs on an annual basis.
Total Bytes Written and Wear
The limited endurance and wear on SSDs does need to be accounted for based on the total data written over time. SSDs used in read-centric applications like backups will unlikely approach the drive writes per day (DWPD) wear limits under normal usage.
For light backup usage under 50GB of data written per day, SSDs should easily provide 5+ years of service life. Monitoring total data written to the SSDs allows predicting replacement cycles based on the manufacturer endurance ratings.
Controller and Cache RAM
SSDs use integrated processors running firmware called controllers to manage all operations of the flash memory and optimize performance. Many also include a small amount of fast SDRAM cache memory, with higher-end models having up to 1GB.
HDDs also rely on onboard processors and cache memory, though in smaller capacities around 64-256MB typically. The controller and cache in both SSDs and HDDs help manage data integrity and access reliability.
Encryption Support
Maintaining security of backup data is critical. Full disk encryption helps prevent unauthorized access if drives are lost or stolen.
Most SSDs and HDDs support the AES encryption standard if enabled. Hardware encryption offloads the intensive encryption/decryption tasks away from the main system processor for efficient security.
Self-encrypting SSDs and HDDs that encrypt all data as it is written are also available. They provide automated encryption without configuration needed.
Rebuild and Repair Time
If RAID data redundancy is used, rebuild times to restore full redundancy after a drive failure are faster with SSDs. Rebuilding 1TB of storage averages:
- SSD – 2 to 4 hours
- HDD – 7 to 10 hours
The faster rebuilds of SSDs minimize time spent in a degraded state with lower fault tolerance. Self-monitoring, Repair, and Telemetry (S.M.A.R.T) capabilities built into SSDs and HDDs also help identify impending drive issues before outright failure.
File System Support
Modern SSDs and HDDs both support a wide range of common file systems used in data storage and backups, including:
- NTFS
- exFAT
- EXT4
- Btrfs
- XFS
Choosing optimized file systems like Btrfs and ZFS provides additional data integrity checks and fault tolerance for both SSDs and HDDs.
Availability of Diagnostic Tools
Major SSD and HDD manufacturers provide free disk health monitoring and diagnostics tools such as:
- Samsung Magician for SSDs
- Western Digital Data LifeGuard for HDDs
- Intel SSD Toolbox
- Seagate SeaTools for HDDs
These perform drive tests and provide tracking of key usage metrics like total data written, temperature, wear leveling, and bad block counts to predict failure risks. They help maximize backup reliability for both SSDs and HDDs.
Hybrid Options
SSHDs (solid state hybrid drives) combine a small SSD with a larger HDD in a single drive, providing a balance of speed, capacity, and cost. The SSD acts as a cache for frequently accessed data while less used data resides on the HDD.
However, hybrids may not be ideal for dedicated backup usage where the fastest SSD speeds are desirable for the most reliable backups. They can be considered for non-critical bulk secondary storage though.
Conclusion
SSDs provide better reliability than HDDs for backup usage in most aspects. Their lack of moving parts, durability, shock resistance, temperature tolerance, speed, and lower failure rates make SSDs the preferred option for modern backup needs.
HDDs still maintain some advantages in maximum capacity and lower cost. But SSD prices are dropping rapidly. For backups under 8TB, SSDs can now provide a good balance of reliability, capacity, and affordability.
In summary:
- SSDs are better for durability, lifespan, shock resistance, and temperature tolerance.
- HDDs have lower long-term magnetic data decay rates when stored powered off.
- SSDs tolerate more challenging environmental conditions.
- HDDs offer much larger maximum capacities for mass data archives.
- SSDs have big transfer speed advantages and handle fragmentation better.
- HDDs maintain a substantial per-gigabyte cost benefit.
- SSDs have around 4-5X lower annual failure rates compared to HDDs.
For backup scenarios requiring high data integrity, frequent backups, archival storage for 3-5+ years, portability, operation in varied environments, or rapid restores, SSDs will likely perform better.
HDDs still work well for infrequent bulk backups of very large capacities exceeding 8TB where slower speeds and transfer times are acceptable. Hybrid SSHDs can also provide a compromise of SSD caching with HDD capacity for secondary backups.
Bottom line – SSDs will provide the most reliable performance for the majority of backup needs today, making them the top choice over HDDs for most use cases.
