On 11-03-14 4:25 PM, Krisjanis Linkevics wrote:
But
formatting may (although it's no guarantee) repair a glitch in an iffy
card and let you continue using it.
-bmw
Some facts and common sense:
SD memory is NAND flash which means the following things:
1) manufacturers ship it with errors already on the chip;
2) it deteriorates over time (with write/delete cycles);
3) it contains software and hardware to detect new errors on the fly and record
information about the bad blocks;
4) said software isolates the card from the outside world - no program writes
directly to the free space on the card.
What formatting these does should be exactly nothing (or equivalent to deleting
files) but formatting is done with a piece of software on the host computer (or
camera) and therefore can introduce more writes/deletes than necessary.
What people formatting cards usually think is that the whole card will be
writeen full of zeros - which - although thankfully not the case - is actually
what you don't want to do - ever (because of the wear and tear).
Now whether cards become bad with time or not is mostly dependant on the
hardware/software controller on the card itself - depending on how good it is
at choosing places to write files and how good it is at marking the bad spots
on the card - the card could either die very fast or live practically forever.
So what card you buy really matters.
Usage - whether you write large volumes of data or routinely "format" the card
with a formatting tool that comes with your operating system and was never intended for
formatting flash memory - comes second. With luck the controller on the card can deal
with your formatting tool and fool it into thinking that the card has been formatted -
although if we look at an empty card that you are formatting to the same file system it
already has and with the same options, there should be no writes at all.
So what this all comes down to is: if it aint broken, don't fix it. If it
breaks, pray to god that you can actually do anything about it - chances are
you can't - at least formatting can only stumble upon errors in a very limited
space at the beginning of the card - and is very much like a blind man trying
to walk into the only tree that's in the middle of a very large field.
kris
Kris, I wouldn't call that a rant, nor do I disagree with any of your
facts and sense.
One point though: when most modern OSes format a FAT block device, they
simply create a new empty directory structure without touching anything
else; the so-called Fast Format. Only a few writes are done, so not too
hazardous to the overall device write allowance. Not too much different
from "del *.*" in fact.
Now if a bad block is discovered on your Flash device while trying to
read the directory structure, I assume that the bad block will
immediately be remapped, but the damage is already done. Not physically
damaged of course, but files could appear to be unreadable, contain
holes, etc. The fix is to format the card and that will replace the
directory structure. Life goes on.
-bmw
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