If you’ve noticed the numerous posts lately on the Datalight blog regarding JEDEC and eMMC, you might be wondering why we’re so excited about this particular standard. There are many features that this “smarter” memory will enable for OEMs; In this post I’ll focus on one of those features in the eMMC specification –secure delete.

Securely deleting information on flash memory is more complicated than it seems. For one thing, files are constantly being moved around to ensure even wear of the flash, resulting in multiple copies of file data on the media. Furthermore, when a file is marked for delete, it is typically not physically deleted, rather the space is only marked as available to be overwritten. Until that happens, the “deleted” data is still present and recoverable on the media. In fact, the University of California San Diego Non-volatile systems lab has produced an in depth study of file deletion on flash memory, where they found significant data still present on the media even after deleting the files. A copy of the report can be found at: http://cseweb.ucsd.edu/users/swanson/papers/Fast2011SecErase.pdf

In order to securely delete a file on raw flash, you must use a controller that will either track every block where the file has been stored, or will overwrite the space the file was stored in each time it is moved. The latter describes exactly the secure erase and secure trim features found in the eMMC 4.41 standard. This means that the hardware will finally be capable of securely deleting files –brilliant! There is just one problem: Who has software to support this functionality? As of this writing, there is no file system which supports the feature. While an application can make a call to the media to delete a file securely, the file system may have a backup copy stored somewhere. Fact is, the file system must support the secure delete capabilities of the hardware in order for these features to function correctly.

If an OEM wants to take advantage of the secure erase and secure trim features, their application will need to communicate with the eMMC driver, which may differ from part to part. As the only software company that is an active member of JEDEC, we are excited offer support for quite a few eMMC features. File system support for secure erase and secure trim will be coming later this summer!

Learn more about Datalight Embedded File Systems

JEDEC, the Joint Electron Devices Engineering Council (see http://www.jedec.org), is a group of manufacturers and suppliers collaborating to create specifications for Flash memory access and parts. The current revision of their specification for Embedded MultiMedia Cards, eMMC, is 4.41, and is available on the website above.

I’m excited to be a part of Datalight and JEDEC, and am looking forward to the upcoming eMMC 4.5 and UFS 1.0 specifications. Datalight is not in the business of manufacturing hardware, of course, but our file system products like to work closely with the underlying driver. Until those products are fully eMMC 4.5 compliant, what can you expect?

The most fundamental thing a Reliance file system needs is a block device that writes data when it says it will. Any data left in a cache or not flushed upon command could be lost data in an unexpected power loss. The Enhanced Reliable Write feature means any eMMC 4.41 or 4.5 flash part will work perfectly with Reliance and Reliance Nitro.

The High Priority Interrupt feature of eMMC basically means that a block device write might pause, reporting back only a partial write. This is fully supported in the Reliance Nitro file system, which will then loop back and continue the write after the HPI is complete.

The Trim feature of eMMC 4.4.1 is being replaced by a Discard feature in eMMC 4.5. The latter fits in more closely with the way Reliance interacts with our own FlashFX product.

Basic functionality (Read, Write, and Erase) is of course supported, and full compliance with eMMC 4.5 is on Datalight’s roadmap, so keep an eye out here for more news soon.