Solid State Drives(SSDs) based on flash memory generally demonstrate lower latencies than the hard disk drives(HDDs), often enabling faster response times. thus can deliver ultra high performance input/output operations per second(IOPS). For random read workloads, SSDs deliver higher throughput relative to HDDs.
There are many types of SSDs on the market, how are they catagoried? Here is some general ideas:
Based on Nand Flash
SLC, or Single Level Cell, allows for the storage of one bit of information per NAND memory cell. SLC NAND offers relatively fast read and write capabilities, high endurance, and relatively simple error correction algorithms. SLC is typically the most expensive NAND technology. With SLC drives each cell is specificed to last for around 100k writes. Reads are unlimited. SLC drives are more suited for enterprise environments because of their durability. They can be cost prohibitive in consumer applications.
MLC, or Multi Level Cell, technology in general is less robust than SLC as there are two bits stored in each cell. If one cell is lost two bits will be lost. With MLC drives each cell is specified to last between 3000 to 5000 writes. The drives are usually available in large capacities and are usually less expensive. MLC based SSDs are being used in enterprise applications deploying smart management techniques such as overprovisioning and endurance management
eMLC, or enterprise MLC is a variant of MLC technology that is harvested from the highest quality portion of the NAND wafer and programmed uniquely to increse erase cycles. eMLC achieves endurance level of 30,000 write cycles, whereas some of the newest MLC only has 3,000 write cycles. eMLC makes a tradeoff to enable this endurance by giving up data retention. eMLC addresses that problem by lenghtening the flash memory chips' internal page programming cycle which creates a better, more lasting data write, but slows write performance. Since eMLC SSDs are somewhere between MLC and SLC on write endurance, their price is usually between the two types. By adding advanced endurance management techniques, this technology can be successfully used in general purpose enterprise applications
There is another type called Enterprise value MLC, provides less write endurance to fit write less but read more applications, see more in Enterprise MLC SSD vs Enterprise value MLC SSD
Based on host interface
SATA SSD are based on the industry standard SATA interface. SATA SSDs provide resonable performance for enterprise servers.
SAS SSDs are based on the industry standard SAS interface. SAS SSDs combine superior reliability, data integrity, and data fail recovery making them suitable for enterprise applications.