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Dynamic Over-Provisioning

ATP Dynamic Over-Provisioning is a unique solution that enables users to configure OP percentage based on actual workloads to optimize performance, prolong SSD life span and ultimately, save costs in the long run. 

Over-provisioning (OP) is a standard industry practice of setting a specific amount of flash storage for controller functions. This space is neither visible nor accessible to the user. Typically, manufacturers set the OP percentage at 7% for client applications, and 28% for enterprise storage applications.

Embedded applications often require very different workloads, so if users are unable to change the OP percentage after the device is shipped, this lack of flexibility may result in higher total cost of ownership (TCO), decreased efficiency, and shorter device usage life.

The Problem: Drive Degradation

Various workloads can dictate the efficiency of data processing and tremendously affect drive endurance, sustained write performance and performance stability. If the storage device came with the manufacturer's pre-configured OP, lack of flexibility in configuring the OP may affect drive performance and longevity. 

Each NAND flash cell can only handle a finite number of write (program) and erase cycles. Two common metrics for measuring SSD degradation are terabytes written (TBW) and write amplification index (WAI). 

  • TBW reflects the estimated life of an SSD based on the total amount of data that can be written on it. The higher the TBW, the longer an SSD lasts. 
  • WAI refers to the actual amount of physical data written to the SSD in relation to the amount of logical data written by the host. In read-intensive applications or high-sequential write cases, WAI can be very low, ideally close to 1. For example, 1 MB of data from the host is written as 1 MB of data on the SSD. In write-intensive applications and random-write cases however, WAI tends to become much higher due to the nature of SSD, which requires that blocks must be erased first before they can be written to. The constant relocating, rewriting, and erasing contribute to the SSD's higher workload, higher WAI, performance degradation and ultimately, shorter endurance.

Figure 1. Write amplification happens when the data that the host intends to write on the SSD becomes larger due to the cycle of relocating data, erasing the whole  block, and rewriting data.

Limitations of Current OP Solutions

The practice of over-provisioning, or reserving SSD space for controller operations like garbage collection and TRIM, helps manage data traffic and mitigates the write fragmentation, thus leading to enhanced performance and endurance. 

Currently, however, devices are shipped with a fixed OP percentage, and actual workloads on-site are not realistically taken into consideration. Such inflexibility eventually causes performance to suffer and leads to shorter usage life.

At the outset, a drive with lower OP might seem to cost lower per gigabyte, as it appears to offer greater storage space to use. However, if the workload continues to increase while OP space is low, this may lead to higher WAI, eventually degrading the SSD faster, lowering TBW, requiring more frequent drive replacements, and thus, more costs in the long run.

ATP Solution: Dynamic Over-Provisioning

The ATP Dynamic Over-Provisioning solution gives users the freedom and flexibility to configure the OP percentage based on assessed actual workloads. OP percentage may be set to 7%, 14%, 28%, even 50% and above, using simple software. 

Higher OP = Better 4K Random Write Performance
The figure below shows 4K random write testing under 7%, 14%, 28% and 50% OP, simulating workloads over extended periods of time. Results show that at lower OP percentages, there were bigger drops in random write speed; inversely, the performance drop was lower at higher OP percentage.

Figure 2. Write performance for 4K random write under 7%, 14%, 28%, and 50% OP. 

Higher OP = Lower WAI 
Different workloads affect performance, leading to various WAI. Higher or lower WAI is a good indicator of performance and workloads. Figure 3 plots the WAI of various OP percentages, showing that OP percentage is inversely proportional to WAI. 

Figure 3. WAI under 7%, 14%, 28%, and 50% OP.

Higher OP = Higher TBW
Figure 4 shows that OP percentage is directly proportional to TBW — the higher the OP percentage, the higher the TBW, which means that the drive endures longer and is able to write more data in its lifetime. 

Figure 4. TBW under 7%, 14%, 28%, and 50% OP.

 
The table below summarizes the effects of different OP configurations on drive performance and endurance.

Item

Lower OP Higher OP

Drive Performance (Random Write)

ê 

é

Sustained Performance Over Time

Worse/Less Steady

Better/Steady

Drive Endurance

ê

é

Table 1. Comparison of the effects of lower/higher OP settings on drive performance and endurance.

The following table shows ATP products featuring the Dynamic Over-Provisioning solution:

ATP Flash Products with Dynamic Over-Provisioning

SlimSATA

mSATA

M.2 

2.5" SSDs

Table 2. Dynamic Over-Provisioning is available on ATP SlimSATA, mSATA, M.2 and 2.5" SSDs
(Images are not to scale.)

Cost Optimization

Lower OP provides more user capacity. It does not, however, automatically mean lower cost per gigabyte. The above test results show that higher OP results in lower WAI, yielding more TBW and therefore, longer endurance. Down the road, the return on investment (ROI) is higher due to more efficient performance and less frequent drive replacements.

Making OP adjustable depending on workload empowers users to optimize performance, endurance and cost. Those who want high performance and longer SSD usage life may opt for higher OP settings. Though extra capacity is traded off and less space is available for storage, they can benefit from the greater efficiency and endurance.


Figure 5. Cost comparison between lower OP and higher OP in terms of user capacity and TBW. The OP setting of around 14% delivers the most advantageous resource allocation benefit in terms of user capacity and TBW.

Different OP percentages can affect SSD performance and endurance. With ATP's Dynamic Over-Provisioning solution, users can evaluate actual workloads and configure the overprovisioned space accordingly using simple software. They have the freedom and flexibility to optimally configure SSDs with 7%, 14%, 28% and even 50% or more OP space for the best-possible performance and endurance. By enabling users to configure the OP setting based on actual needs, the ATP Dynamic Over-Provisioning solution maximizes the performance and life span of the SSD, translating to greater productivity and better operational efficiency.

Dual Configurable Storage Solutions: Mid-Density and Dynamic Over-Provisioning

The Dynamic Over-Provisioning solution is part of ATP's Dual Configurable Storage Solutions. Together with ATP Mid-Density solution, they address the limitations of fixed storage configurations. The tandem state-of-the-art solutions empower users with the freedom to choose and configure storage based on real application needs.
 
By enabling users to configure the OP setting based on actual needs, the ATP Dynamic Over-Provisioning solution maximizes the performance and life span of the SSD, translating to greater productivity and better operational efficiency. ATP's mid-density storage products, on the other hand, deliver optimal cost-per-gigabyte, so users pay only for what they do need. Mid-density also minimizes the cost jump from lower to higher capacity, giving users a wider range of choices based on their needs, resulting to more cost-effective resource allocation.
 
Contact an ATP Representative to know more about ATP's Dynamic Over-Provisioning and Mid-Density solutions.
 

 


 
 

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