SD/MMC cards, a year later
tiagomnm at gmail.com
Thu Aug 19 13:59:40 EDT 2010
Thanks for the update. Can you disclose the brands of the mentioned SD
It's always useful to know what not to buy.
I'm assuming none of these cards don't have static wear levelling. Did any
manufacturer provide you details on that or are they only using spare blocks
Any plans for the use of NILFS? It seems to help with wear levelling,
although it is not a completely circular log FS.
On Thu, Aug 19, 2010 at 4:24 AM, John Watlington <wad at laptop.org> wrote:
> Our experiment with SD/MMC cards as main storage continues.
> One frustration has been the rate of change in the SD industry.
> The dominant model from a vendor in a particular size and speed
> may only be in production for three or four months before being
> superseded. Vendors are reluctant to properly inform Quanta of
> changes which might require retesting. The result is that SD card
> certification is an ongoing process.
> A disturbing trend has been the increased error rates and
> decreased device lifetimes brought by higher density devices.
> And these are occuring throughout the industry.
> A batch of 2GB class 2 microSD cards obtained a year ago from a
> particular manufacturer averaged around 10 TB written before
> failing, with few transient errors. A batch of 2GB class 2 microSD
> cards from the same manufacturer today failed with more than
> half corrupting their FS after only 1TB of writes. The devices
> wear out around 2-4 TB of writes. I'm seeing the same error
> distribution on 4GB parts from the same manufacturer, and
> similar problems of early filesystem corruption from other
> manufacturers as well.
> Of the last five SD card models we've tested, we rejected three
> of them for failing to survive 3 TB of writes. In some size/speeds,
> we only have a single vendor/model qualified --- always on the
> brink of being end-of-life'd.
> While the Armada 610 SOC being used in XO-1.75 does have a
> "raw" NAND Flash interface, it's design faces the same problem
> as the CaFE in XO-1 --- it will only be useful for today's (yesterday's)
> NAND Flash parts. Each new generation tends to introduce higher
> demands on the (hardware implemented) error correction algorithms.
> Nonetheless, we are going to try testing it with UbiFS and
> considering whether any durability improvement justify the
> increased price (now up to 2x) and built-in obsolescence of
> using raw NAND chips.
> On the positive side, the SD interfaces on XO-1.5 have been
> exercised extensively and we have eliminated the bit errors that
> plagued some XO-1 motherboards.
> Overall, the industry is even more behind microSD than a year
> ago, although eMMC (roughly the same protocol and all the same
> automated wear levelling issues but 8 bits wide with multichip modules
> soldered directly to the PCB) is gaining acceptance in the cell-phone
> Devel mailing list
> Devel at lists.laptop.org
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