Enterprise MLC (eMLC) is a type of multi-level cell (MLC) flash that has been enhanced to accommodate more write cycles than consumer-grade MLC flash offers.
Individual consumer MLC cells can only provide 3,000 to 10,000 write cycles, while enterprise MLC cells can handle 20,000 to 30,000 write cycles. In the enterprise, eMLC can serve as a compromise between inexpensive MLC flash and very expensive single-level cell (SLC) flash.
Typically, eMLC is 2-bit, while consumer MLC flash is 3 or 4-bit. In general, the more bits a flash cell has, the fewer write cycles it will have. Because eMLC flash media has more program-erase (P/E) cycles than consumer MLC, it has greater endurance and can tolerate the types of workloads that enterprise applications require.
A primary focus of eMLC vendors is to further improve write endurance and make MLC flash as reliable and long-lived as SLC flash. There are a number of techniques that vendors are using to improve write endurance, including:
Distributing input/output (I/O) evenly across the entire flash drive, an approach called wear leveling.
Improving the unrecoverable bit error rate (UBER) by creating better algorithms.
Prolonging the time before the drive becomes unreliable by over-provisioning the flash media.
Reducing write amplification.
Related glossary terms
A write cycle is the process of recording data on a NAND flash solid state storage device. Write cycles are also called program/erase (P/E) cycles.
Once flash solid state storage media has reached a steady state, blocks of unnecessary data are erased automatically when new data is written. This clean-up process, which makes room for new data, is called garbage collection. Because garbage collection is invisible to the end user and cannot be suppressed, the erase operation is dropped from every day speech and the cycle is simply identified as a “write cycle.”
There are a finite number of NAND flash write cycles.
Example: If there is a 100 GB SSD and it's write cycles are 8760 then it means that it can write 100 GB Data per hour, every hour for full year.
Total IO per year = IO per hour x 24 x 365 / SSD size
= 100 GB x 24 x 365 /100
= 8760 GB
Solid-state storage program-erase cycle
A solid-state-storage program-erase cycle is a sequence of events in which data is written to solid-state NAND flash memory cell (such as the type found in a so-called flash or thumb drive), then erased, and then rewritten. Program-erase (PE) cycles can serve as a criterion for quantifying the endurance of a flash storage device.
Flash memory devices are capable of a limited number of PE cycles because each cycle causes a small amount of physical damage to the medium. This damage accumulates over time, eventually rendering the device unusable. The number of PE cycles that a given device can sustain before problems become prohibitive varies with the type of technology. The least reliable technology is called multi-level cell (MLC). Enterprise-grade MLC (or E-MLC) offers an improvement over MLC; the most reliable technology is known as single-level cell (SLC).
Some disagreement exists in the literature as to the maximum number of PE cycles that each type of technology can execute while maintaining satisfactory performance.
MLC, typical numbers range : 1500 to 10,00 PE-cycle-per-block
E-MLC, numbers range up to approximately : 30,000 PE cycles per block.
SLC, devices can execute up to roughly : 100,000 PE cycles per block.
External Link:
eMLC : http://searchsolidstatestorage.techtarget.com/definition/enterprise-MLC-eMLC
Write Cycle : http://searchsolidstatestorage.techtarget.com/definition/write-cycle