by Anton Shilov
02/21/2011 | 09:41 PM
Transition of NAND flash memory manufacturing to 25nm fabrication process seems to have run into issues. Some customers of OCZ Technology have complained about lower capacities of solid-state drives based on 25nm memory and also their lower performance. But Micron Technology, the maker of 25nm NAND flash memory, claims that the memory itself has the same reliability as previous-generation and competing makers of SSDs are to be blamed.
"You have probably seen some of the forum buzz about new 25nm NAND SSDs. One of our SSD competitors rolled one of their existing models to new 25nm NAND, but they created a slower, lower-capacity drive - and did not change the model number or any of the marketing to acknowledge these shortcomings. Their customers are upse). The end result of all this has created some negative perceptions about the quality of 25nm NAND, which is really misplaced. It is possible to build great SSDs with 25nm NAND, but you do have to be deliberate about your process and objectives (it also helps to have inside knowledge about how that NAND works)," said Justin Sykes, a spokesperson for Micron, in a blog post.
In order to sustain reliability, endurance and life expectancy of new SSD lineups based on 25nm chips from Micron, OCZ Technology had to reduce their user-accessible capacities so that to reserve more bits for over-provisioning. Unfortunately, OCZ failed to correctly disclose that fact to end-users. On the other hand, Micron itself agrees that early batches of multi-level cell (MLC) NAND flash are less reliable than "mature" batches, which is why for SSD makers it is not easy to maintain both capacity, life expectancy and performance of all drives.
"There is nothing wrong with over-provisioning (reserving some of the NAND capacity for better performance and durability), but the drive label must state the capacity the user has access to. [...] SSD enthusiasts are aware that new NAND designs start out at lower endurance cycle counts than the previous generation, and are sometimes wary of next-generation SSDs as a result. But cycle counts don’t necessarily translate 1:1 to drive endurance specs - good NAND management is the key. We specify SSD endurance in total bytes written (TBW). The 25nm C400 offers the same endurance as the C300 for the 128, 256 and 512GB models - 72TB TBW," said Mr. Sykes.
According to Micron, it has taken the reliability of its own next-generation RealSSD C400 solid-state drive "very seriously and have gone to great lengths to develop advanced firmware algorithms that manage the NAND". However, it looks like the early adopters of the technology, Micron's direct clients, might not have access to certain technology peculiarities of the new memory and had to balance performance, endurance and capacities based on the actual situation.
"Being NAND developers gives us the unique ability to design end-to-end SSD quality as a complete system, alongside our NAND design team," stressed the spokesman for Micron.