Is it true that a SD/MMC Card does wear levelling with its own controller?

I work for a company that used to be a member of the SD association, we are familiar with the 2.0 (SDHC) spec. The SD card spec has NO entry for wear leveling. That is completely dependent on the SD manufacturer to handle that if they so choose. We have seen that some likely do, while others very much do not (beware the super cheap knock-off SD cards). SDXC may have changed that to include wear leveling, but I am unsure of that. Unfortunately the only way to really show that is to get your hands on the official spec. You can find it online most likely, but the SD association really wants you to pay for it.

As a side note, taking a 2GB card and writing it beginning to end over and over again averages about 10TB before the card is dead and no longer is writable. Also, SD cards will not let you know when data is bad, i.e. wont return an I/O error like a PC harddrive will. This might not be an issue for embedded designs as 10TB is a LOT of data, but it could be a factor for someone.

It's true! MicroSD cards contain a NAND flash chip bonded to an (ARM) microcontroller encapsulated in some black plastic. http://www.bunniestudios.com/blog/?p=898 explains.

At the end of the follow-up post http://www.bunniestudios.com/blog/?p=918 Bunnie posits integrating the controller probably costs less than testing the flash ahead of time.

Quoting SanDisk's SD card product manual: "1.9 Wear Leveling. Wear leveling is an intrinsic part of the erase pooling functionality of the SD Card, using NAND memory." You can read the whole thing in the datasheet for a SanDisk brand card.

Yes, SD/MMC cards have controllers that do wear leveling. If they didn't, you could destroy one in a matter of minutes with the wrong write patterns.

That's actually a problem for some embedded projects. There's absolutely no way (apparently) to know what sectors might be wear leveled at any time, so a power cycle at the wrong time can destroy data anywhere on the card, no matter where you THINK you're writing. (don't ask how I know :) )

SD cards must be used with a system that guarantees a clean system shutdown (or at least that writes are allowed to complete), or data loss will (eventually) result.

EDIT

The problem is that the wear leveling process is entirely hidden. ANY sector on the disk could be moved at any time (swapped with the page written), and if power was to fail in the middle of that process that random sector could get corrupted.

While there ARE reasonably safe ways to implement this move, it's not in any spec so you can't trust that the card will do it. You could test one card, have it work, then the manufacturer could change the implementation without changing the part number and you're screwed.

From testing, my SD cards' controller does NOT do this in a safe manner at all.

I may look into a "high reliability" SD card I saw advertised specifically for power failure tolerance... but then you have to trust the manufacturer to do that correctly, and I don't. I really want direct control over page erases. I'm still trying to figure this one out.