Write Balancing

How Controllers Maximize SSD Life

Tempus FugitHow do controllers maximize the life of an SSD?  After all, MLC flash has a lifetime of only 10,000 erase/write cycles or fewer and that is a very small number compared to the write traffic an SSD is expected to see in a high-workload environment, especially in the enterprise.  Still, MLC is becoming the norm in the enterprise.

How do they do that?

This is where SSD architects really earn their pay.  There are eight basic techniques that The SSD Guy knows of to extend SSD life beyond Continue reading

Standards for SSD Endurance

The Grand Canyon - An Extreme Example of WearSSD endurance is an important concern that stands in the way of SSD adoption in a number of data centers.  Since flash is new to the enterprise (and computing systems are a new market for flash) important issues including wear specifications still need to be hammered out.

Until flash SSDs started experiencing adoption in standard computing environments, nobody really anticipated the difficulties that would arise from flash’s inherent wear-out mechanism.  Most flash manufacturers erroneously believed that Continue reading

SSD Garbage Collection

garbage cansOne of the thorniest issues in SSD design how to manage erasing blocks that are no longer in use.  That’s saying a lot, because NAND flash presents so very many difficult challenges like wear leveling, bad block management, error correction, and write amplification.

The difficulty stems from the fact that all of today’s software was written for HDDs which don’t behave like the flash in an SSD.  An HDD can over-write existing data with new data.  In a flash SSD, a block must be erased before being over-written and this can take a half a second – a huge amount of time in the world of computing.  Since the software doesn’t accommodate flash’s “erase-before-write” needs, the controller inside the SSD must take care of this bit of housekeeping.  Unused and unerased blocks are moved out of the way and erased in the background.  This is called the “garbage collection” process. Continue reading