No surprise on memory
jg at laptop.org
Thu Dec 18 14:39:39 EST 2008
On Thu, 2008-12-18 at 09:13 -1000, Mitch Bradley wrote:
> John Gilmore wrote:
> > Swapping to the soldered-in NAND chips is a very bad idea. It will
> > tend to wear them out rapidly. Even if you use load-leveling software
> > (e.g. swapping to a file in a jfffs2 filesystem), the problem is that
> > if you do start wearing out serious numbers of flash blocks, the
> > laptop becomes toast; it requires a soldering iron and spare chips to
> > fix it.
John, do the math: for the current chips (single level cells), life is
of order 10^5 cycles. So you have 10^5 gigabytes of writing. This
takes *a long* time.
Swapping is not an insane idea, once you have wear leveling. We don't
do it now because JFFS2 cannot support swapping, and we don't have a
wear level beneath the file system.
UBI and Ubifs fix this, and it is something we can consider.
> Well, maybe it's not as bad as all that. When the NAND wears out, then
> you can buy the SD card, thus deferring that purchase and taking
> advantage of Moore's law in the interim.
Lots of people tend to forget, however, that warm (and/or cold) salt air
is a serious issue in many of the places we have to go. Any connector
tends to die under these circumstances.
> Note that I'm not advocating in favor of soldered NAND - in fact I've
> been one of the leading proponents of migrating to an SD-based storage
> solution. I'm just pointing out that, if you're willing to buy an SD
> card now (which is necessary for the SD-based swap solution), then you
> are probably willing to buy one later.
Soldered down SD, however may be an intermediate point; may fewer wires
than a conventional chip.
Jim Gettys <jg at laptop.org>
One Laptop Per Child
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