The SLC vs MLC solid state drive debate has been going on for quite some time now. The cost vs. performance of either technologies has been brought down enough to merit serious consideration when putting together a storage system.
As with any technological comparison, there are always trade-offs depending on which solid state drive technology you choose.
SLC vs MLC
Table of Contents
|Higher $$/GB = More Expensive
|Lower $$/GB = Cheaper
|Lower Wear Rates
|Higher Wear Rates
|Higher Write Performance
|Lower Write Performance
From this basic comparison, you might draw the conclusion that single-level cell solid state drives are superior and the performance boost justifies the cost. However in practice, you may not notice the differences as clearly. SLC vs MLC is not the main topic of discussion on storage sales. Usually these discussions are directed towards the memory controller of the solid state drive.
Flash memory cells all suffer from wear. The material begins to degrade because of the constant erasing or programming of the cell by applying a voltage. Each time one of these actions occur, a charge is trapped in the transistor’s gate dielectric and causes a irreversible change in the characteristics of that cell. After a finite amount of write/erase cycles, the cells will fail.
SLC uses a single cell to store one bit of data. MLC uses a single cell but can interpret 4 digital states. This makes the area denser and cheaper to produce, but it leads to lower write/erase endurance of the drive. Basically while an MLC might be rated at 9,000 write/erase cycles, an SLC cell might last ten times that before it fails.
This finite write/erase cycle of solid state drives can be prolonged through developed technologies and techniques. Wear-leveling is a technique that aims to spread out the write cycles around the solid state drive so the cells wear more evenly. On-device deduplication – reduces the volume of data written to the cells. Write optimization – stores data writes so that numerous write operations can be grouped together to reduce the number of write operations. These technologies and techniques are incorporated in the enterprise MLC solid state drives. Most of these techniques are controlled by the memory controller.
The implementation of the device usually determines the technology. High-speed databases, whose measured in terms of its performance will be matched to the appropriate technology. You may see more MLC solid state drives in consumer-grade products and also in the enterprise where performance, while essential, is not the primary factor.
The Future of Solid State Drives
Solid state drives may never replace spinning disks. The cost of making an SSD may never fall as low as disk because of manufacturer limitations.