which file system for sd card?
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
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