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Preview: Comments on: On MicroSD Problems

Comments on: On MicroSD Problems

bunnie's blog

Last Build Date: Tue, 24 Apr 2018 02:56:20 +0000


By: Prashant

Thu, 17 Mar 2011 12:00:28 +0000

I tried this with linux mint on a dell latitude E6410. I do not seem to find any of these folders. ‘/sys/block/mmcblk0/device/’ or /sys/devices/platform/cpuxxx-mmc.n/mmc_host/mmc0' Can anybody help me with this

By: wookey

Tue, 01 Mar 2011 14:28:20 +0000

This is a fascinating discussion. I am a fan of access to the real flash and filesystems designed to deal with that (I've been involved with YAFFS since its inception). I am distrustful of the idea that the (incredibly cheap) flash controller in my SD card will do a better job than a properly written driver and filesystem. This is particularly true because that controller is written exclusively to do a good a good job of running a FAT filesystem, mostly writing large contiguous flies as fast as possible (i.e the camera/media player use case), because that is still 99% of the market. That means it only track 2 'write areas' and it keeps extra bad blocks for the file allocation table at the front of the device. That's terrible for ext3, where the journal is at the end of the drive and you need more than 2 'write areas' in use at once. The firmware in the controller is not at all interested in being good with ext2 or ext3 or btrfs, and Arnd Bergman has done some realy good characteristation recently of the problem: If we could talk to the flash directly then it wouldn't matter that the manufacturers only cared about FAT and cameras. Sadly that's not the way the market is going. SD flash is now _much_ cheaper than solder-down 'real' flash, and the solder down-stuff is getting built-in controllers too: 'eMMC', so it seems that raw-flash filesystems are not the way of the future. Which is OK, but they do need to work properly, and right now many of them work very badly indeed in the sort of use cases we are interested in. Reliability is terrible, speed is poor. You do make a good point bunnie, that the disk drive people have done a great job of putting a lot of caching and firmware between you and the drive platters which does all sorts of magic and we're not finding that a problem, but we have a long way to go until the SD people get their act together and do such a good job that their algorithms are filesystem-neutral, and we still get reasonable lifetime out of the flash. It would be great if we could talk to the controller manufacturers/firmware writer people and get cards made that worked better with real filesystems. After all - it's just an ARM7TDMI so writing some code for it is no big deal. YAFFS would just about fit in that 128K :-) (that probably isn't the best plan, but it would be really interesting to try). I have no idea how we get to talk to the right people about this - the use of real filesystems on SD and eMMC is only going to grow and we need to get beyond the 'FAT is the world' view many still seem to have. The controller does have some advantages over a linux driver in that it has better bandwidth to the raw flash and more info on manufacturing/performance details. But it also has the major problem that the power can be yanked at any moment, and what you should do about that depends a lot on the use-case, which is why UBI has a lot of tuneability in terms of how long you are prepared to wait before hits the real flash. Collaboration and good work in this area is no doubt hampered by a load of crappy patents that will have been filed on 'anything sensible you can do to improve flash error rates and performance'. That probably makes the firmware authors nervous about opening up their code.

By: Army Strong

Sat, 19 Feb 2011 17:49:17 +0000

I just purchased one of these irregular cards off eBay from seller idobiz09 (John Paladino, It looks identical in every way to your sample #1 picture. Needless to say, I could not get it to work properly no matter what I tried. The seller wouldn't refund or exchange, but I got a refund by filing a claim through eBay. I wanted to see if anyone else was having trouble with the same card so I typed in the lot number and found your article. Thanks for doing the research and posting your findings.

By: doodles

Sun, 13 Feb 2011 14:57:52 +0000

very interesting read, thanks for sharing!

By: oklahoma by owner

Mon, 07 Feb 2011 16:54:16 +0000

thanks for the research, i'm bookmarking this site and signing up for the feed.