which file system for sd card?

Fernando Martins fernando at cmartins.nl
Sun Jan 25 14:49:15 CET 2009

Sean McNeil wrote:
> Neither of those filesystems are appropriate for sd cards. They have 
> wear leveling logic that is not necessary or a good thing as it is 
> already done in firmware for sd. An efficient journaled filesystem not 
> designed for memory devices (like ext3) would be best.
A quick net reading tells me that wear leveling works by counting writes 
and remapping sectors. Still wearing doesn't go away. It's also not 
clear what are the limitations of wear leveling. How much space 
remapping requires (or is reserved beforehand) and thus how many sectors 
can be remapped and whether it also suffers from wearing problems itself.

Although wearing is not important for my specific use (mostly static 
storage of maps), I think a journaled file system essentially duplicates 
the writes in terms of data and might have some extra writes for extra 
data structures. Thus, speculating a bit, a journaled file system uses 
more space, causes more writings and can put more strain on wear 
leveling (the journal, in addition to the file system data structures).

Another issue, actually the most important for this use, is read 
performance. FAT has the advantage of requiring simple logic but 
indexing it's poor (I think it does a sequential access on each relevant 
directory table). I guess it also depends a bit on the FAT 
implementation (I've read subjective claims that Linux implementation is 
not the best). Unfortunately a quick search didn't return really 
interesting benchmarks.


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