Solid state drives (SSDs) have become increasingly popular in recent years due to their fast performance and lack of moving parts. However, one downside to SSDs compared to traditional hard disk drives (HDDs) is that data recovery is much more difficult, if not impossible, on SSDs. There are several reasons why SSDs cannot easily recover lost or deleted data.
How SSDs Store Data Differently Than HDDs
First, it helps to understand how SSDs store data differently than HDDs. HDDs store data on spinning magnetic platters. When data is deleted on a HDD, the reference to that data is removed from the file system but the actual data remains in place on the platters until it is eventually overwritten by new data. This allows recovery software to scan the platters and retrieve the deleted data as long as it has not yet been overwritten.
SSDs, on the other hand, use flash memory chips to store data. Flash memory cells can only be written to a limited number of times before they wear out and can no longer reliably store data. To extend the life of the drive, SSDs use a process called wear leveling to distribute writes across all the cells evenly. This involves moving data around to different locations on the drive as cells wear out.
When data is deleted on an SSD, the reference is removed just like on a HDD. However, the SSD controller will then immediately erase the flash cells at the physical location that previously held the data. This is done both for security reasons and to prepare those cells to be written to again in the future. So the deleted data is erased almost instantly after deletion.
TRIM Command Erases Deleted Data
Another barrier to data recovery on SSDs is the TRIM command. When you delete a file on an SSD, the operating system informs the SSD controller using the TRIM command. This allows the SSD to immediately perform garbage collection to erase and reuse any cells that contained deleted data.
The TRIM command results in permanently destroying any trace of deleted files on an SSD. Even data recovery software is unable to retrieve anything that has been TRIMmed. This is quite different from HDDs where deleting files does not immediately affect the recoverability of the deleted data.
Garbage Collection Erases Deleted Data
SSD controllers also perform garbage collection from time to time to free up storage space. This involves relocating any data from blocks that have a high degree of invalid pages and erasing those blocks so they can be reused. The garbage collection process will permanently destroy any deleted data residing in those blocks.
Garbage collection occurs in the background and can happen at any time without the user explicitly deleting files. So even if you do not manually delete files on an SSD, the background garbage collection process can still result in deleted files being permanently erased over time.
Wear Leveling Moves Data Around
As mentioned earlier, SSDs use wear leveling to distribute writes evenly and prolong the life of the drive. However, this constant reorganizing and moving of data makes it nearly impossible for recovery software to locate and recover deleted files. The files are not stored in predictable locations based on logical block addressing like on HDDs.
Wear leveling ensures that data is constantly being rewritten to different physical locations on the SSD. Over time, previously deleted data can be moved and overwritten to a point where data recovery becomes impossible.
Data Recovery Success Depends on Timing
Because of the above factors, the success rate for data recovery on an SSD depends largely on the timing. If you act quickly before too much new data is written and triggers garbage collection, you may be able to recover recently deleted files using data recovery software.
However, the longer you wait, the more likely it is that the deleted data has been TRIMmed, erased by garbage collection, or overwritten by wear leveling. This makes recovery progressively more difficult the longer the drive operates after deleting files.
Logical Failures vs Physical Failures
Data recovery companies often differentiate between logical failures and physical failures of a drive. Logical failures relate to deleted or corrupted files where the underlying hardware is still functional. Physical failures occur when the physical components of the drive fail, such as electrical problems or failed read/write heads.
Data recovery from physical drive failures involves techniques like drive imaging, component swapping, and specialized clean room disassembly. This type of recovery has similar success rates between HDDs and SSDs.
However, for logical failures, the unique way SSDs handle deleted data makes recovery much less feasible compared to HDDs. So while physical recovery success is similar, logical failure recovery rates are far lower on SSDs.
How Deleted Data is Overwritten
When the OS issues a delete command, the SSD will mark the associate blocks as empty and erase the data in those blocks. This happens due to:
- The TRIM command telling the SSD to erase unused blocks
- Garbage collection erasing blocks with high invalid page counts
- Wear leveling migrating data to distribute writes evenly
This erased space will then be reused when new data is written. The new data overwrites and destroys any traces of the old deleted data.
This overwrite process continues in the background as you use your SSD. The collective impact makes data recovery progressively more difficult over time.
SSD Controllers Actively Prevent Data Recovery
SSD controllers and their firmware are designed specifically to both maximize performance and increase the lifespan of the drive. As a byproduct, this also makes data recovery extremely difficult.
Some of the ways SSD controllers actively prevent recovery include:
- Efficiently handling the TRIM command to immediately erase deleted data
- Actively performing background garbage collection to free up storage space
- Wear leveling algorithms distribute writes so no single cell wears out
- Bad block management isolates damaged NAND cells to improve reliability
While these processes are beneficial for performance and longevity of the SSD, they are detrimental for data recovery purposes.
Full Disk Encryption Further Complicates Recovery
If an SSD employs full disk encryption, that adds yet another barrier to successful data recovery. The encryption applied by the SSD controller scrambles all the data written to the NAND flash chips. The encryption key is required to decrypt and read back the data.
So even if you managed to get past the other challenges with deleted data on SSDs, the encryption applied by hardware-based full disk encryption solutions can make recovery essentially impossible.
Recovering an SSD with Failed Controller
If the SSD controller hardware itself fails, that poses additional challenges for recovery. The controller manages all the flash memory and runs the firmware that oversees the crucial processes like wear leveling, garbage collection, and encryption.
Getting data off failed SSD controllers is very difficult and may require specialist data recovery experts. They might transplant the flash memory chips into a working controller to get access to the raw NAND flash data. However, this is an expensive and low success rate process.
Why HDDs Allow More Data Recovery
Given all these obstacles, you may wonder why data recovery is much more viable on traditional hard disk drives (HDDs) compared to SSDs.
There are a few key reasons:
- HDDs store data on physical platters so it remains in place until overwritten
- No TRIM command quickly erases deleted data on HDDs
- Wear leveling is not needed on HDDs so data location is more predictable
- Garbage collection does not occur on HDDs
- Full disk encryption is less common on HDDs
This means deleted files remain in their original physical location on the drive platters. As long as the deleted data has not yet been overwritten by new data, recovery software can find and restore deleted files by scanning the platters.
So HDDs allow for deleted file recovery even days, weeks, or months later unless the deleted space has since been reused for new files. SSDs are a stark contrast, making even quick deleted file recovery difficult.
Is Data Recovery Impossible on SSDs?
While SSDs make data recovery exponentially more challenging compared to HDDs, it is not always impossible.
As mentioned earlier, the timing of the deletion and recovery attempt is critical. The sooner you act, the higher the chances of success. The longer an SSD operates after deleting files, the lower your chances become.
DATA RECOVERY TABLE
| Time After Deletion | Chance of Recovery |
|---|---|
| Within minutes | High |
| Within hours | Moderate |
| Within days | Low |
| After days/weeks | Very Low |
Specialized data recovery firms that invest in SSD training and technology offer the highest chances of successfully recovering deleted data from SSDs. But customer expectations need to be set properly based on the relatively low success rates.
Tips to Increase Chance of SSD Data Recovery
Here are some tips that can help maximize your chances if you need to attempt data recovery on an SSD:
- Stop using the SSD immediately after deleting files to prevent overwriting deleted data
- Avoid programs that write lots of data like video editing software
- Do not run the operating system optimization tools like defrag on the SSD
- Clone the SSD or make a sector-level image backup before attempting recovery
- Use a data recovery company specializing in SSD/flash recovery
Can SSDs Have Lower Failure Rates?
It is true that SSDs can have lower failure rates than HDDs in some cases. HDDs have more mechanical parts like actuator arms that can physically fail. SSDs primarily use flash memory chips and a controller board.
However, SSD failure rates can still be high if low-quality NAND flash or controllers are used. High-end enterprise SSDs designed for 24/7 operation have very rigorous testing and use the highest grade components. This results in extremely low failure rates compared to consumer-grade SSDs.
Even with higher reliability, SSDs are still susceptible to logical failures like accidental deletion or corruption of files. And unlike HDDs, this logical failure data cannot easily be recovered on SSDs. So lower physical failure rates do not necessarily equate to better recoverability of lost or deleted data.
Is Data Encryption Mandatory on SSDs?
Full disk encryption is not mandatory on SSDs. However, some SSD controllers support hardware encryption capabilities to encrypt all data written to the drive by default. Many popular consumer SSDs like Samsung 870 EVO have built-in 256-bit AES hardware encryption.
Encryption provides protection against unauthorized access if a drive gets physically stolen. But it also adds additional hurdles to data recovery in the event of drive failure or accidental deletion. The encryption key is required to decrypt data off the SSD before any recovery can be attempted.
Manufacturers may provide a recovery key along with retail SSDs that have default hardware encryption. Properly backing up this key is crucial. Otherwise, data recovery becomes impossible on encrypted SSDs without the decryption key.
Does TRIM Work Differently on HDDs vs SSDs?
Yes, TRIM is handled very differently between traditional hard drives and solid state drives when you delete files.
With HDDs, deleting files only removes the file system references to those files. The actual data remains in place on the physical platters until the areas are overwritten by new data.
On SSDs, the TRIM command tells the SSD controller to immediately erase the flash cells corresponding to the deleted files. The data is erased as soon as you hit delete. No remnants of deleted data remain on the SSD cells.
So TRIM results in instantly permanent destruction of data on SSDs. On HDDs, TRIM does not affect the recoverability of deleted files since the data remains intact on the drive platters.
Conclusion
While SSDs provide lightning fast performance and greater physical reliability than hard disk drives, they also hinder the recoverability of lost or deleted data. This occurs due to fundamentals of NAND flash memory and how SSD controllers manage the storage media.
TRIM, garbage collection, wear leveling, and encryption all contribute to making data recovery difficult on SSDs. The chances diminish drastically over time as deleted files get overwritten with new data.
In most cases, preventative backups are the only way to protect against permanent data loss on SSDs. Attempting recovery after deletion has very low success rates. Understanding the limitations of SSDs is important when choosing storage media and managing data protection schemes.
