To avoid a scenario where the SSD is filled to full capacity with invalid pages, over-provisioning is used by the FSP garbage collection function as a temporary workspace to manage scheduled valid page merges and reclaim blocks filled with invalid pages.
Any reclaimed pages/blocks are then added to the over-provisioned capacity to accommodate write operations from the FSP and maximise performance during peak traffic load as the performance impact of reading, erasing, modifying and writing all valid pages back into an already partially full block filled with invalid pages can be a slow exercise.
The garbage collection operates independently of the operating system and is automatically triggered during periods of low activity, periodically or by issuing the respective ATA Data Set Management TRIM command.
An always-available number of empty blocks via the over-provisioned capacity assists in maintaining effective wear-levelling on the NAND Flash as the FSP intelligently redistributes write operations across all NAND Flash memory cells evenly without impacting the SSD’s overall performance during peak traffic loads.
Together with LSI SandForce DuraWrite technology, the ATA Data Set Management TRIM command can add to dynamic over-provisioning by reclaiming any invalid pages and unused user capacity using on the fly data compression/reduction techniques. This reduces the actual footprint of presumed valid data and NAND Flash wear.
As shown in Figure 3, after a presumed 25 Gigabytes Microsoft Windows Vista operating system and Office 2007 application installation, SandForce DuraWrite technology has effectively reduced the total writes committed from the host computer to the NAND Flash to 11 Gigabytes. 
Figure 3. The Power of DuraWrite™ 
In Figure 4, we show a scenario using 28 per cent over-provisioned capacity with no ATA Data Set Management TRIM support. A large portion of presumed valid data written by the host computer is left unoccupied and unused on the actual NAND Flash.
With the use of DuraWrite data reduction technology, the original data was compressed to occupy less capacity and ATA Data Set Management TRIM allowed the SSD to reclaim the presumed valid data on the drive up to 50 per cent for use with the pre-allocated OP capacity.
Figure 4. Dynamic Over-provisioning 
Without the use of dynamic over-provisioning on SSDs, the Flash Storage Processor has to rely solely on using a pre-allocated static over-provisioned capacity or reduced capacity Dynamic Random Access Memory (DRAM) for managing the NAND Flash.
To manage this data reduction technology via the FSP, some over-provisioning of the NAND Flash is allocated to the FSP to handle the target data. The compressibility of the target data is described by the associated entropy level and data with an entropy level of 100 per cent is typically completely random and cannot be compressed further.
Using varying entropy levels of sustained 4KB Random Write transactions which typically represent the highest write amplification and most arduous performance exercise due to their operational behaviour on NAND Flash, we can observe and measure the effect increased over-provisioning has on the overall endurance and performance of the SSD.
Figure 5 shows a considerable increase in Random Write (4KB Sustained) performance across all entropy levels of data with each percentage increase in over-provisioning. Entropy levels of 75–100 per cent show the biggest increases in performance with each proportional increase in over-provisioning and illustrate the importance and benefit of over-provisioning not only on data transactions with low entropy levels, but also the critical importance of larger over-provisioning in increasing sustained performance for highly random/higher entropy data.
Figure 5. Random Write performance vs. percentage Over-provisioning 
Figure 6 shows the same transactions respective of write amplification and the critical role over-provisioning plays in lowering the write amplification for data with higher entropy levels to increase NAND Flash endurance.
The lack of suitably sized over-provisioning would eventually decrease the compression efficiency, sustained random write performance and have a real user-perceivable impact via slower operating system/application performance and eventual premature wear out of the SSD due to a higher write amplification, especially in scenarios involving data with high entropy levels.
Figure 6. Random Write WA vs percentage Over-provisioning