Is Overprovisioning Good for SSD?
Imagine having a sleek, lightning-fast SSD that effortlessly handles your data storage needs. But what if I told you there’s a way to supercharge its performance and boost its lifespan? Enter SSD over-provisioning, the secret weapon that takes your solid-state drive to new heights. In this blog post, I’ll unravel the mysteries behind over-provisioning and unveil its hidden powers.
Think for a second
Have you ever wondered why some SSDs outshine the competition in speed and endurance? The answer lies in their ability to go beyond their stated capacity, setting aside a hidden reserve for optimization and longevity. Over-provisioning, the Jedi mind trick of the storage world, is the practice of allocating extra space beyond the visible capacity of an SSD.
But why should you care about over-provisioning? Picture this:
- Improved performance,
- Reduced write amplification,
- Better garbage collection,
- Increased durability.
Sounds like a dream come true, doesn’t it? By delving into the world of over-provisioning, you can unlock these benefits and more.
What is Overprovisioning?
Over-provisioning of an SSD (Solid State Drive) refers to the practice of allocating a portion of the drive’s capacity beyond what is advertised or made available to the user. In other words, it involves setting aside a certain amount of storage space on the SSD that is not accessible to the user for regular data storage.
Over-provisioning aims to improve the overall performance, reliability, and lifespan of the SSD. It allows the drive to maintain a higher level of performance and efficiency over time, mitigating the impact of wear and tear associated with normal usage.
When an SSD is over-provisioned, the unused storage capacity is utilized by the SSD’s controller and firmware to perform various optimization tasks. These tasks include wear leveling, garbage collection, and error correction.
1) Wear Leveling:
Flash memory cells within an SSD have a limited lifespan and can only endure a finite number of write operations before they start to degrade. Wear leveling spreads the write operations evenly across the drive, ensuring that all cells are used balanced. With over-provisioning, there is a larger pool of cells available for wear leveling, reducing the strain on individual cells and extending the overall lifespan of the SSD.
I wrote an entire article about this wear leveling. Please refer it at What Does SSD Wear Level Mean?
2) Garbage Collection
SSDs use a technique called garbage collection to free up space that is no longer in use. When files are deleted or modified, the SSD must erase the old data cells before they can be rewritten. Over-provisioning provides additional free space that can be used for garbage collection, allowing the drive to perform these operations more efficiently and maintain better performance.
3) Error Correction
Flash memory is prone to errors like bit flips or data corruption. SSDs employ error correction algorithms to detect and correct these errors. Over-provisioning enables the SSD to allocate more spare memory for error correction codes, enhancing the driver’s ability to maintain data integrity.
By allocating a portion of the SSD’s capacity for these optimization tasks, over-provisioning helps prevent performance degradation and ensures that the drive operates at a consistently high level. It also helps to maintain sufficient free space on the drive, as SSDs tend to perform better when they are not filled to their maximum capacity.
It’s important to note that over-provisioning is typically handled automatically by the SSD’s firmware and controller. Users do not need to allocate space for over-provisioning manually. However, it is worth considering when selecting an SSD, as drives with higher over-provisioning ratios may offer better performance and longevity.
Unlike traditional Hard Disk Drives (HDDs), Solid State Drives (SSDs) operate by storing electrons on NAND cells when data is written. However, the stored data cannot be directly overwritten or erased on NAND flash. SSDs handle writing and erasing operations in different units called pages and blocks, respectively.
This means that multiple programs and erase operations cycles are necessary to manage and store data effectively. As these cycles are repeated, some electrons become trapped between cells, leading to wear-out and durability issues over time. This phenomenon, known as cell wear-out, imposes physical limits on the lifespan of NAND flash memory.
Given these constraints, it becomes crucial to manage NAND effectively to extend the overall lifetime of the SSD. Repeatedly writing data to the same area causes those cells to wear out more quickly. To prevent this, wear-leveling is employed to distribute write operations across different regions evenly.
By swapping blocks that have undergone many program/erase cycles with free blocks, wear-leveling ensures that all cells are utilized more evenly. This helps users maximize the lifespan of their SSD under normal operating conditions.
Due to the nature of NAND flash memory, overwriting existing data is impossible without first erasing it. This erasure process slows down the overall write performance of an SSD since erasing is carried out on a block level while writing is done on a page level. To mitigate the impact on write performance, a technique called garbage collection (GC) is implemented.
GC consolidates valid pages into a single location and erases blocks containing invalid pages, creating free blocks within the SSD. However, in some cases, garbage collection can interfere with the host’s write operations, potentially resulting in slower performance. To ensure the smooth operation of the firmware (FW) feature responsible for GC, it is essential to have free space available on the SSD. This allocation of extra space is known as over-provisioning (OP).
How To Calculate OP Ratio?
When calculating the over-provisioning (OP) ratio for an SSD, we use a simple formula:
OP (%) = ((Physical Capacity – User Capacity) / User Capacity) * 100.
Let me illustrate this with an example:
Suppose we have a 128 GB SSD, out of which 120 GB is available for user data storage, and the remaining 8 GB is allocated for over-provisioning. We can determine the OP ratio as follows:
OP (%) = ((128 – 120) / 120) * 100 = (8 / 120) * 100 = 0.067 * 100 = 6.7%
In this scenario, the over-provisioning ratio is 6.7%. This means that 6.7% of the total physical capacity of the SSD is reserved for optimization and management purposes, while the remaining 93.3% is made accessible to the user for data storage.
Over-provisioning enhances the SSD’s performance, reliability, and lifespan. By setting aside a portion of the drive’s capacity, the SSD’s controller and firmware can effectively carry out wear leveling, garbage collection, and error correction processes. This ensures better longevity, data integrity, and overall efficiency of the SSD.
Remember, the OP ratio can vary depending on the SSD model and manufacturer, and it is worth considering when selecting an SSD based on your specific requirements and use case.
What are the advantages of increasing OP?
When it comes to the advantages of increasing the over-provisioning (OP) of an SSD, several key benefits exist.
1) Improves the efficiency of Garbage Collection
As data is written over the entire space of the NAND, the performance of random writes tends to diminish compared to sequential writes. Random writes that involve smaller data operations mix valid and invalid pages within blocks. This data mixing within blocks leads to frequent garbage collection (GC) operations, ultimately resulting in decreased performance.
However, increasing the OP allows more free space on the SSD that remains inaccessible to the host system. This surplus space improves the efficiency of GC, leading to enhanced performance and sustained speeds. Consequently, the overall performance of the SSD is improved.
2) Increase the Lifespan of the SSD
In addition to performance advantages, increasing the OP also positively impacts the lifespan of the SSD. Internal operations like GC cause the number of writes to NAND memory to exceed the number of writes from the host system. This imbalance increases the Write Amplification Factor (WAF), representing the ratio of host writes to NAND writes.
A higher WAF value indicates a greater amount of unexpected NAND use, potentially shortening the lifespan of the SSD before reaching its specified total byte written (TBW) limit. By providing sufficient OP space, the efficiency of internal NAND operations is improved, leading to reduced NAND usage. This reduction in NAND usage helps mitigate the risk of premature wear and extends the overall lifespan of the SSD.
3) Increasing the daily workload per day (DWPD)
Moreover, increasing the OP has the advantage of increasing the daily workload per day (DWPD) usable during the warranty period. By improving the efficiency of internal NAND operations and reducing the strain on NAND memory, the SSD can handle higher daily workloads without compromising its reliability or lifespan.
This means that users can utilize the SSD more intensively within the warranty period, confident in its ability to maintain optimal performance and meet their demanding workload requirements.
Types of Overprovisioning
Regarding overprovisioning in SSDs, there are three main types to consider: inherent, vendor-configured, and user-configured.
1) Inherent Overprovisioning
Every SSD has a certain amount of inherent overprovisioned capacity for various purposes. This capacity is reserved for the following:
- Controller’s Firmware: A portion of the capacity is allocated to the firmware that manages the SSD’s operations and functionality.
- Failed Block Replacements: In the event of block failures, spare blocks are utilized to replace them, ensuring data integrity.
- Vendor-Specific Features: SSD manufacturers may allocate a portion of the capacity for specific features or optimizations.
The inherent overprovisioning results from the difference between binary and decimal notation used to measure data amounts and capacities in SSDs. For example, an SSD might be labeled as 500 gigabytes (GB) but actually have a capacity of 500 gibibytes (GiB). The additional capacity in gibibytes is reserved and inaccessible to the host computer. The host system can only utilize the reported capacity, which in this case would be 465.7 GiB or 500 GB.
This inherent overprovisioning is crucial for the SSD’s overall performance and reliability. It caters to essential functions such as garbage collection, wear leveling, TRIM command execution, and other background processes that optimize and maintain the drive. However, the SSD controller can only access this reserved capacity and is hidden from the user and host system.
2) Vendor-Configured Overprovisioning
SSD manufacturers may also allocate additional capacity for specific purposes, particularly to accommodate write-intensive workloads. Beyond the inherent overprovisioning, this additional capacity typically ranges from 7% to 28% or even more, depending on the manufacturer’s design choices.
Like inherent overprovisioning, this added capacity is not accessible to the host system and is reserved exclusively for the SSD controller.
3) User-Configured Overprovisioning
In certain cases, users can further overprovision their SSD by utilizing the available user-accessible capacity. This can be achieved using a vendor-provided tool or by creating a separate partition that reserves a defined space on the drive.
It’s important to note that user-configured overprovisioning differs from inherent or vendor-configured overprovisioning. Inherent and vendor-configured overprovisioning reserves capacity that is invisible to the user and host system, while user-configured overprovisioning utilizes the unreserved user capacity.
By implementing user-configured overprovisioning, users can allocate additional space on the SSD to enhance performance and improve the drive’s endurance for specific use cases or workloads.
Q : How much should I Overprovision my SSD?
A : When considering the amount of overprovisioning (OP) for your SSD, allocating around 15% to 20% of the total SSD capacity is generally recommended. This allocation ensures that there is a sufficient amount of reserved space to enhance the performance and longevity of the SSD.
It’s important to note that the optimal OP percentage may vary depending on the specific SSD model, its intended usage, and your individual needs. Therefore, it’s always advisable to consult the manufacturer’s guidelines or documentation for any specific recommendations or considerations related to OP for your particular SSD.
Q : Is Overprovisioning still necessary?
Absolutely, overprovisioning is still necessary when it comes to SSDs. It plays a crucial role in enhancing SSD performance and increasing the overall lifespan of the drive.
Overprovisioning allows SSDs to maintain consistent and reliable performance over time. By allocating a certain portion of the SSD’s capacity as reserved space, the drive has room to perform crucial background operations like garbage collection, wear leveling, and other maintenance tasks. This reserved space ensures that these operations can be carried out efficiently, preventing performance degradation and extending the lifespan of the SSD.