Nasta writes: > >I know youve sort of answered this before, but the one thing that gives me > >cause for concern is the long-term reliablity of CF media. And how are we > >going to notice - apart from in the most unpleasant way - that its natural > >life is reaching its close? > > CF cards use flash memory chips which can take at least 1 million writes to > the same location - and the internal controller does not let the bytes be > written to the same place if it can avoid it. Instead, the writes are > 'staggered' - a sector that is overwritten is actually declared empty and > another is written instead, than that one is 'soft-remapped' to be at the > same space as it's previous 'version'. Previously written sectors are only > rewritten if it cannot be avoided due to running out of space. All of this > is actually quite easy to do on a block oriented device, unlike one with > purely random writes. > This in effect means that the CF will allways last at least 1 million > writes, and more probably, far more. For instance, if you only kept > rewriting one single 512 byte sector on a 32M card, the staggered write > principle will extend the life of the card to 1M * size_of_card / > size_of_one_sector, in this example to 64 billion writes!!! A hard drive > would be HARD pressed to get even close to that figure. Of course, reading > a CF is unlimited. This is quite different than hard disks, where both > reading and writing slightly reduce the remaining lifetime, primairly of > the mechanical parts. > Finally, writing flash memory AUTOMATICALLY implies verification, which > does not happen on hard disks. On hard disks, corrupt data recovery is > attempted (and not always successful!) on read. On a CF card, write errors > are immediately diagnosed and the sector is remapped. There are a few spare > sectors on the card. Once these run out, the card will return errors on a > write attempt and the user will immediately know that something is wrong. > Assuming there is an alternative place to store data, it will not be lost. > I suppose iy's obvious that a CF is much more sturdy than a hard drive, by > virtue of not having any moving parts, being very light weight and > generating next to no heat :-)
Im convinced ;) Per
