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

Kishore kitts.mailinglists at gmail.com
Sat Jan 17 12:59:12 CET 2009

On Saturday 17 Jan 2009 12:51:10 pm Carsten Haitzler wrote:
> On Sat, 17 Jan 2009 11:31:35 +0530 Kishore <kitts.mailinglists at gmail.com>
> babbled:
> http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv016.cgi?read=92882
> (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:
> http://wiki.openmoko.org/wiki/Booting_from_SD
> 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.

Thanks for the information. With such widespread use of USB flash drives which 
are really cheap and of large capacities I guess the technology has gotten 
cheaper. I recollect that the concept was called flash translation layer or 
something like that. Anyway, it also justifies the higher price paid for the 
bigger brands. A good reason for me to recommend the bigger brands over the 
many other cheaper ones in the market! :)

> > 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.
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