[Om2008.12] Adding swap space can stop app crashes

Carsten Haitzler (The Rasterman) raster at rasterman.com
Sat Jan 17 08:21:10 CET 2009

On Sat, 17 Jan 2009 11:31:35 +0530 Kishore <kitts.mailinglists at gmail.com>

(search for wear levelling - message # 4):

Part of the SD spec is something called "wear leveling". This attempts to
spread writes out to previously unused physical sectors and maps them to their
proper logical sector number. Properly implemented, you wont wear out a fixed
directory sector. The spec and flash chips also supports bad block replacement. 

even openmoko's wiki:


SD cards are supposed to support wear leveling, but this can not be guaranteed
for all vendors.


i can keep hunting down more references - but its meant to be part of the spec.
cards should do it - some may do it better than others (ie name brands - cost
more, lifetime warranties), and some el-cheapo ones may skip it to cut costs.

> On Saturday 17 Jan 2009 6:13:37 am Carsten Haitzler wrote:
> > as such the sd-card should be doing wear-levelling for you as it maps
> > logical to physical addresses and has an erase pool with extra blocks to
> > play with. it can be "improved" by a better fs aware of the algorithms that
> > card uses - but each card may be different depending on maker...
> > wear-levelling is part of the spec for sd and hidden behind the sd access
> > interface - so card manufacturer will determine quality of this... so spend
> > your money wisely and get a good reputable sd card from the major names
> > that come with lifetime warranties.
> Are you sure of this? I remember from a few years back for a project at work 
> it was understood that compact flash was the only card that did wear
> levelling internally and that is why it also was so much more expensive. I
> know most of USB memory sticks do it these days so it cant be that expensive
> any more. If true then this is really good news. One will not need to bother
> too much with having to use a file system which does wear levelling for any
> project that uses a SD card.

------------- Codito, ergo sum - "I code, therefore I am" --------------
The Rasterman (Carsten Haitzler)    raster at rasterman.com

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