On Saturday 17 Jan 2009 12:51:10 pm Carsten Haitzler wrote: > On Sat, 17 Jan 2009 11:31:35 +0530 Kishore <[email protected]> > 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. -- Cheers! Kishore
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ Openmoko community mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/community
