FORTASA BLOG

Flash Card and SSD Endurance Measurement - Lifecycle Calculation and Estimate - Part 1

Every customer looking to integrate SSD or Flash Memory based storage system is keen on knowing the useful life he can expect from the chosen storage product. The worst thing that could happen is that the Flash drive reaches the functional end of life and stops working frustrating the user and mandating an expensive service call.

SSD Reached Its Endurance Limit

Endurance, or how many program/erase cycles the Flash device can handle over the product lifetime, is a key metric that determines the effective service life of a Flash device and defines the amount of written data that it can can sustain before reaching the end of its rated life. In SSDs or Flash cards there is NOT a one-to-one relationship between the number of host writes and the actual physical program/erase cycles performed to the NAND Flash media. Due to the nature of Flash Controller data management algorithm, not all NAND blocks  reach their end of life simultaneously.

READ MORE

MLC NAND Flash Supports Industrial Temperature Range - -40oC - +85oC

Many end applications for Industrial Storage Products such as SSDs and Flash cards require full Industrial temperature range operation. That means the the storage device needs to be fully functional and operate reliably even under the most extreme temperature conditions. An industry convention proliferated to differentiate between a typical consumer operation of 0oC to +70oC (Standard Temperature) and Industrial requirement of -40oC to +85oC (Industrial Temperature).

Upto a few years ago the only Storage Products capable of full Industrial Temperature compliance were the ones manufactured using the Single-Level Cell (SLC) NAND Flash. The SLC Flash offered not only full Industrial Temperature compliance, but also a very high endurance rating of 60K to 100K cycles. The only drawback to using SLC NAND based SSDs was the high cost of the solution.

At the same time, the Multi-Level Cell (MLC) NAND Flash was being aggressively driven into a multitude of high volume consumer applications such as Digital Cameras, MP3 players, Cellular Phones and Tablet PCs. MLC Flash made most sense in these consumer "disposable" application as while the endurance rating of typically 3K cycles and temperature support were minimal, the component price was almost four times cheaper than the equivalent capacity SLC component.

READ MORE

SSD MTBF Rating - Meaningless in Flash Drive Reliability Estimate

Many Flash Drive manufacturers provide a Mean Time Between Failure (MTBF) rating as an estimate of an SSD life expectancy. Typically this rating is >2,000,000 hours for an SLC (Single Level Cell) NAND based SSD or >1,000,000 hours for an MLC (Multi-Level Cell) based SSD. While at a first glance 1 Million hours (114 years) of life expectancy seems like a huge overkill for a typical application, in reality an MTBF number is not representative of the realistic expected usage of the Flash SSD.

MTBF is a theoretical formula based on the sum of the Mean Time To Failure (MTTF) rates of the individual components used in a specific SSD design.

Formula to calculate MTBF for a Flash SSD, Card or Module

READ MORE

Write Amplification - Cause for Diminished Reliability in Flash SSD

Write Amplification is a major contributor to the reduced life expectancy of an SSD. Unlike a conventional HDD, Flash based SSD can’t simply write new user data on top of the previously recorded data. Instead, flash memory requires an erase and subsequently a re-write cycle to be issued to program the new information. Typically when the system needs to only update a single page of data, the flash controller has to read the full erase block size of data into the read buffer, update the desired page in the read buffer, erase the original block and re-write the updated block of data back to the Flash media. The same update process needs to occur not only to the data information itself, but also to the file table structure that links the data pages into a full information file. Therefore, a single page of data update actually mandates multiple Flash media writes. This process is commonly called – Write Amplification phenomenon.

Considering that Flash Media has a finite number of program/erase cycles as specified by the component Flash supplier, the SSD-wide Write Amplification phenomenon of increasing the number of program/erase cycles, significantly reduces the useful life of the SSD. Additional system requirement of Wear Leveling to spread the Flash Media usage by re-writing between static and dynamic data adds to the Write Amplification factor.

READ MORE