Re: SD card longevity Message #7 Posted by James M. Prange (Michigan) on 19 May 2006, 2:41 a.m., in response to message #6 by James M. Prange (Michigan)
Now that I've thought about this a bit more, utilities such as MS
ScanDisk and Norton Disk Doctor probably do a good check when
doing a read-only test, but perhaps not so good for a read-write
test. Such utilities presumably work a (logical) cluster (or
perhaps sector) at a time, but it seems to me that with the card's
wear-leveling remapping the blocks when it writes, the next
logical cluster isn't necessarily the next physical cluster.
What's more, when a cluster is marked as "bad" in the FATs, that
would be the logical cluster, and which physical sectors that maps
to would change because of the card's wear-leveling.
On the other hand, Juan reports that ScanDisk was able to fix his
CF card. Perhaps CF cards don't do any wear-leveling? Or maybe
attempting to write to (or read from) bad areas caused the card to
"notice" the defects and map them out?
Regarding defragging, it seems to me that this typically writes a
lot of clusters, and given that writing eventually "wears out" the
flash memory, may actually do more harm than good.
Regards, James
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