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NAND memory characteristics

Esteemed Contributor III

There were 2 references to the characteristics of NAND memories as used in SSDs as I watched the online videos of the new SSD drive with a 500Mb/sec transfer. The first reference was to the need to run a program (recommended daily) to keep the access speed up, on the SSD drive. Regarding this point, is this the equivalent of a defrag program for a mechanical drive, where there are holes as files are read and written, and this puts them back together again and maybe even optimizes the written space and the blank space?

Secondly, there is the mention of backing up the drive because of the limitation of how many times a NAND can be written-to or read, before it starts going bad. What exactly is this limitation? How does it occur? Is this the identical to the failure rate of any solid state DIMM memory carded into the computer memory slots, based on mean-time-to-failure, or is something else going on here?

A third question, not covered in the videos is,"Is this non-volatile memory, or is the memory held alive by an onboard supercap or other voltage source?


Esteemed Contributor III

There is no program that is needed to run daily to maintain SSD performance. Newer operating system support a command called TRIM which tells the SSD when to clean up deleted pages.

SSDs are not HDDS.... SSD intentially fragment data across multiple NAND chips for performance and wear leveling.

NAND chips eventually wear out after 3000-5000 writes. The layers in the cell eventually wear out. However, this should not be a big worry for most home/desktop use.

There is a specification called "Total Bytes Written" (TBW) but I do not see one listed for the 510.

However, here's an example of a near worst case scenario for most people:

You have a 120GB SSD with 128GB of NAND.

The NAND has only 3000 cycles.

The write amplification is 1.2x.

That means you would have to write about 20,000GB worth of date before you use up the reserve space.

The majority of users write less than 10GB a day to their disk.

That means your SSD is good for at least 5 years and again is worst case for most people.

Using more conservative numbers, you are looking at around 7-10 years before you run out of reserve space. However, the worn-out pages are still readable AND the rest of the drive is still usable. Basically, it isn't that big of an issue for most home users.

SSD use NAND memory which are non-volatile.

Esteemed Contributor III

Thank You. In terms of archive of data, it seems like just when I've just found the perfect solution by digitizing the media of human interaction of sight and sound, so that there is no degredation to the 'nth' playback, I find out that the media I store it on won't last past 5 years. Even the dye in the CDs and DVDs and Blu-rays, being orgainic have a shelf-life, like every other organic compound. I have books that are 40 years old, and I can still read the pages and see the colored pictures. It is a shame that this kind of burned-in information can't be kept undegraded for at least as many years when translated down on a nano level.

Esteemed Contributor III

As with everything in the world of computers, there are endless details, and Duckie gave you the overview of SSD longevity. The NAND cells of an SSD have a finite number of write operations they can endure, before they no longer will be writeable. Duckie's numbers are conservative, I have seen the number of writes as 10,000. While the write operations may be used up, the NAND cells may still be read many, many more times. Not permanent, but better. CDs and DVDs may last 50 to 100 years, if you can find a device to read them 100 years from now, which would include all storage media we use today.

Except for one that is, that being the printed paper page, which has yet to be beaten for longevity, given the right conditions of storage, and ease of being read.

Esteemed Contributor III

Gary, I want to point out that NAND is not rated to store data indefinitely. I believe NAND will lose its charge after 10 years or so.