Garbage collection and TRIM for SSDs

Non-volatile Flash memory is increasingly used in harsh environments like factories where severe
vibration can impact operability. SSDs are more robust than traditional HDDs, offering better energy
efficiency, longer lifespans, faster access times, and better read performance.

However, Flash memory is a write-once and bulk-erase form of data storage. This requires a garbage collection mechanism that sorts good data into available blocks. This ensure efficient disk usage but can reduce performance if not managed correctly.

At this point we need to explain a bit more how flash memory is organized in SSDs and how data gets written or erased. 

• Memory in SSDs is usually managed in blocks and pages. 
• One block consists of several pages. 
• Data will be written page by page but can only be erased as block unit.

InnoDisk employs a linear-access optimized garbage collection along with the TRIM command for optimal read/write operations and data integrity.

Garbage collection involves removing stale data from pages and rewriting the data into newly erased blocks (Figure 1). If a free block is empty or the system is idle, the SSD performs garbage collection on that block.

This process of garbage collection involves reading and rewriting data to the Flash memory.

A new data write from the host will require a read of the whole block, a write of the parts of the block which still include valid data and then a write of the new data.

This can significantly reduce the performance of the system.

This is where the TRIM command comes in.

Figure 1: Good data is sorted from stale data in two separate blocks. The data is rewritten into another block containing only the good data

TRIM enables the SSD controller to skip invalid data instead of moving it. Naturally, this frees up a significant amount of resources and extends the lifespan of an SSD by reducing erase and write cycles on the SSD.

All Innodisk SSDs incorporate "Garbage Collection". 

The following product series also support TRIM for better performance:

• SATA25000
• InnoRobust II
• Evergreen

We hope you found this post interesting. 

If you would like to know more about iCell and Innodisk, please send an email to sales@score-electronics.com or look in the Innodisk section on our webpage. 

Innodisk has published a white paper about iCell technology and is available on request.