Re: [ts-7000] Re: Microdrive / Type II CF?

["Don W. Carr" <>]

Ok, I plan to buy a 2 Gig SD card for data logging, which should take
at least 6 months to fill at one sample per second while the train is
running. I did not realize that the SD and CF cards had internal
electronics for wear leveling and bad block management. What is the
best file system to use? I would think ext3 might be a good option. Don.

On 6/1/06, Jesse Off <> wrote:

--- In "Don W. Carr" <> wrote:

> We need to create a HOWTO for doing datalogging to flash memory.
Even if you
> had to buy new SD cards every five years, it might still be cheaper
and more
> reliable than purchasing a mini hard drive.
>
> Don.

This is exactly what we've found.  The super-miniaturized mechanical
guts of a microdrive do not lend themselves well to high MTBF.  They
use a lot of power and run hot being so small.  The intended workload
has a very small duty-cycle as they are designed to be powered off and
idle most of the time.

SD and CF have internal bad block management and wear leveling
algorithms that go on in the controller of the card itself.  Those
electronics make traditional filesystems like FAT or EXT2 no so bad on
flash.  Also, not many people can argue that modern SD or CF running
EXT2 or EXT3 is too slow anymore-- the hardware ASICs on the CF/SD
cards are quite fast and effective at what they do.

JFFS2 and YAFFS couple the bad block management and wear leveling to
the filesystem design itself which is partially the reason their scope
is limited to a particular type of raw flash chip technology (nand,
nor, 2k page nand, etc...).  The methodology of a flash translation
layer underneath a standard block filesystem and the good algorithms
for it are mostly protected from GPL/Linux implementation by a patent
minefield and the perceived opportunity for speed and design
perfection by coupling the two distinct tasks (wear leveling/bad block
management and UNIX filesystem) together in one uber-filesystem.

//Jesse Off

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-- 
Dr. Don W. Carr
J. G. Montenegro 2258
Guadalajara, Mexico
+52-333-630-0704
+52-333-836-4500 ext 2930

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