Re: Smoke and mirrors?
This is a non-issue.
All silicon devices have yield problems due to defects that occur during manufacturing. Various processes are used to minimise the impacts of such losses on production, since lower yields drives up device costs.
On RAM devices, at the design phase, additional columns are added to memory devices and then during the post manufacturing test phase the devices health is assessed and there is a one-time process that blows fusible links within the chip to permanently disable failed columns, hence disabling them. After that, some of the spare columns are configured, again with fusable links to make them assume the address of the failed column, thus resulting in a fully functional device again.
As density increases, the number of failures on a device will increase fairly linearly. I guess it now makes more sense to map out larger regions and this results in the approach detailed in the article.
There is nothing wrong with this. The same technique is used in widely in the industry. Some examples are
CPU's are shipped with complete cores disabled when they failed during manufacturing and nobody cares since they get a cheaper CPU.
The same approach is used on EEPROM (NAND and NOR types), although the process differs. NOR flash (the more expensive ones) are shipped defect free and has the same approach of mapping out bad pages with some spares that are already present in the device.
NAND flash (i.e. the cheaper one) are shipped with defects present and visible and a process to allow the host processor to determine where the bad pages are and manually map around them. On Linux and embedded systems, there is the Unsorted Block Image File System (UBIFS) that handles this process. To ensure that the bad block map its self is reliable - since failures can statistically occur anywhere, the same approach of replacement pages is used on a small number of the first pages in a NAND flash, again to ensure increase yield.
Similarly, hard discs (of the spinning type) use the same approach with some spare sectors, these are placed in a number of regions across the disk surface so that fairly similar seek / access times can be achieved. Again, these are silently mapped in as bad sectors occur or grow on the underlying media. You can see this in the SMART metrics for the discs.
SSD's use the same approach as EEPROM's listed above.
I'm sure there are other examples, but this is just the list of what springs to mind. So, nothing to see here other than higher yields and lower costs for everyone, which is a good thing.
Biting the hand that feeds IT
