Solid state drives (SSDs) have become increasingly popular in computers and other devices due to their faster speeds and lack of moving parts compared to traditional hard disk drives (HDDs). However, some people wonder if SSDs can develop bad blocks like HDDs do. Here is a look at whether SSDs can have bad blocks.
What are bad blocks?
Bad blocks are sectors or groups of sectors on a drive that can no longer reliably store data due to physical damage or manufacturing defects. When a modern HDD encounters a bad block, it locks the block so it won’t be used and remaps the data to a spare area elsewhere on the disk. This helps prevent data loss or corruption.
HDDs are mechanical devices with platters that spin and read/write heads that move across the platters to access data. They are more prone to physical damage that can cause bad blocks, such as:
- Head crashes that damage the platters
- Motors seizing up
- Shock damage from drops or vibration
- Wear and tear over time
SSDs have no moving parts and instead store data in NAND flash memory chips. They are less susceptible to physical damage. However, they can still develop bad blocks in some situations.
Causes of bad blocks in SSDs
Bad blocks in SSDs are most often caused by:
- Manufacturing defects – Imperfections in NAND flash memory cells or interconnects caused during manufacturing. This may lead to cells or areas that cannot retain data reliably.
- Write/erase cycles – SSDs can only withstand a finite number of writes to their NAND cells before they wear out. Too many cycles can cause cell degradation and bad blocks.
- Read disturbs – When data is read from a NAND cell, nearby cells are also activated slightly. Excessive reads to one area can alter charge levels of adjacent cells, causing errors.
- Write disturbs – Similar to read disturbs, writing data can slightly affect the charge state of nearby cells over time.
Other possible causes include power outages or surges during writes, overheating, and cell oxide breakdown over very long periods.
How SSD controllers handle bad blocks
SSD controllers have advanced error detection and correction features to find and manage bad blocks, including:
- ECC – Error correcting code can detect and repair a certain number of bit errors on the fly.
- Spare area – Extra flash capacity is set aside to swap in for failed blocks.
- Wear leveling – Writes are distributed across all cells to prevent premature failure in overused areas.
- Bad block mapping – Any uncorrectable blocks are locked out and remapped similar to HDDs.
- Garbage collection – Recovers unused space and consolidates data to eliminate errors.
These mechanisms help minimize the impact bad blocks have on performance and longevity. Most users will never experience issues even if some bad blocks develop.
Can bad blocks cause data loss in SSDs?
SSDs are designed so that a few bad blocks will not directly cause data loss. When a block cannot be read or written successfully, the SSD will remap it to a spare area. The data should remain intact.
However, there are scenarios where bad blocks may result in data loss:
- The spare area fills up faster than the SSD can remap blocks
- Too many simultaneous block failures overwhelm ECC capabilities
- The SSD controller fails, disrupting crucial management functions
- A power loss occurs during a write operation to a bad block
To avoid data loss, it’s a good idea to regularly backup important data stored on an SSD. Also be aware of the health status reported by your SSD’s monitoring software.
How to check for bad blocks in SSDs
SSDs have S.M.A.R.T. monitoring capabilities that track statistics like bad blocks. Software tools can read a drive’s S.M.A.R.T. data to check for issues. Some tools that can scan for bad blocks include:
- Windows – Disk Management, Hard Disk Sentinel, CrystalDiskInfo
- macOS – Disk Utility
- Linux – smartctl, GNOME Disks, Disks
These will check attributes like “Media and Data Integrity Errors” and “Uncorrectable Errors” to give an indication of bad blocks. Current pending/remapped blocks may also be visible.
It’s also possible to perform read/write tests on an SSD and manually look for problems. But this is not generally recommended as it will degrade the drive faster with unnecessary use.
Can bad blocks be repaired in SSDs?
Unfortunately, it is not possible to repair bad blocks in SSDs. NAND flash memory cells wear out after repeated use, so they cannot simply be made usable again.
The SSD controller has mechanisms to work around bad blocks. But the only way to truly fix bad blocks is to replace the failed NAND flash chips within an SSD. Most consumer SSDs have their chips soldered in, making repairs impractical.
Professional data recovery services may be able to swap chips on some drive models. But otherwise, the SSD would need to be replaced if bad blocks reach concerning levels.
How many bad blocks are normal for SSDs?
It’s normal for SSDs to develop at least some bad blocks over their lifetime, usually beginning after the drive has endured significant write cycles.
Manufacturers design SSDs to continue operating properly with a certain percentage of bad blocks. For example, enterprise-class SSDs often list 1-3% of NAND storage space reserved for remapping blocks.
For a 1TB SSD, this would mean up to 10-30GB of space for spare blocks. Consumer drives have less spare area, but can still tolerate a small number of bad blocks.
While thresholds vary between models, excessive bad blocks usually indicate an SSD is nearing the end of its usable life. Sudden surges can also indicate hardware problems.
Typical bad block percentages at end of SSD life:
| SSD Type | Bad Block Percentage |
| Consumer/PC | 5-10% |
| Enterprise | 10-30% |
Ideally, bad blocks should remain below 1-2% on consumer SSDs. Higher amounts will reduce available capacity but may still be usable if performance is less critical.
Does TRIM help avoid bad blocks in SSDs?
Enabling TRIM on your SSD is recommended to help minimize bad blocks. TRIM is a command the operating system sends to the SSD to notify it which blocks of deleted files no longer contain valid data.
This allows the SSD controller to perform garbage collection to wipe these blocks and make them available again for writing new data. TRIM helps improve write performance and endurance by avoiding unnecessary writes.
If TRIM is disabled, the deleted blocks are not flagged to the controller. New writes will have to erase and overwrite these invalid areas first. This contributes extra write cycles that can potentially wear out cells and develop bad blocks faster.
Can SSDs develop bad blocks due to inactivity?
Inactivity itself does not directly cause bad blocks in SSDs. Unlike HDDs, SSDs have no moving parts that can seize up from sitting unused for long periods of time.
However, data retention of NAND flash cells does slowly degrade over time regardless of drive activity. SSDs rated for 1-year data retention could see some cell charge leakage after a few years of no power cycles.
This effect is much more pronounced at high temperatures and could eventually produce uncorrectable errors. But at normal ambient temperatures, data loss is unlikely even over many years of inactivity.
Do SLC, MLC, TLC, and QLC SSDs get bad blocks differently?
SSDs using different types of NAND flash memory have different susceptibility to bad blocks:
- SLC – Highest endurance but rarely used today due to cost
- MLC – Moderate endurance, older technology
- TLC – Lower endurance but most common in modern SSDs
- QLC – Lowest endurance, used mainly for high-capacity drives
TL;DR – SLC has the highest tolerance for writes while QLC wears out fastest. But all NAND types can eventually develop bad blocks with enough use.
Overall SSD design and controller algorithms also play a big role in longevity. Affordable TLC and even QLC drives today can still far outlast typical consumer workloads.
Do PCIe/NVMe SSDs get bad blocks more than SATA SSDs?
PCIe and SATA are interface connections that do not inherently affect an SSD’s susceptibility to bad blocks. NVMe is a protocol that can utilize PCIe bandwidth.
NVMe SSDs allow much faster read/write speeds than SATA models. This performance comes from parallel access to the NAND flash chips and queues of commands.
In terms of endurance, both PCIe/NVMe and SATA SSDs use similar NAND flash memory. At the same capacity, they will exhibit fairly comparable lifetimes and gradual development of bad blocks.
That said, NVMe drives at the very high end may use extra optimizations for intense workloads that can extend drive lifespan slightly. But for typical consumer use, SATA and NVMe SSDs will have quite similar bad block behavior.
Conclusion
In summary, SSDs can develop bad blocks, but not to the same extent as mechanical HDDs. Their spare capacity and controller algorithms help minimize the impact on performance and longevity.
A small number of bad blocks is normal over time, especially for TLC/QLC NAND flash equipped SSDs. But sudden surges can indicate a problem. Monitoring tools can check for issues, but bad blocks cannot be repaired, only remapped. Backups are still important to prevent data loss.
With good SSDs lasting many years for consumer workloads, bad blocks should not be a major concern. But being aware of their causes and limitations is helpful for getting the longest lifespan from your SSD.
