So, completely guessing here...
What you call "sector" the data-sheet calls Block, right?
Thus, if it's a x8 device, the block size is 16K + 512bytes spare.
For an x16 device, the block size is 8K + 256 xpare.
But for calculation sake, just use the 8K or 16K
Thus, for a 256M of NAND, and a
1) x8 NAND - you have 16,384 K block size = 16384 blocks per 256MB of NAND
[i.e. 268,435,456 (256MB) / 16384 (block size) = 16384 (total blocks)]
2) x16 NAND - you have 32,768 blocks per 256MB of NAND.
Double the total numbers of blocks
So, lets assume worst case situation.
Lets use the larger block size, (an x8) NAND
Lets also assume we can write the NAND ONLY 50,000 times, instead of 100,000 times [50% of total life]
That would mean in worst case, we're talking about 819 million sector writes before we'd reach what Hynix claims is only 50% of the total write cycles for the device. (i.e. 819,200,000 sector writes) [16384 * 50000 = 819200000]
If you go to 75% of total write cycles, it would be 1.228 BILLION sector writes. (i.e. 1,228,800,000 sector writes)
If you go to 100% of total write cycles, it would be 1.638 BILLION sector writes. (i.e. 1,638,400,000 sector writes)
And those are the most conservative. If you have an x16 NAND, double those figures.
So, I'd guess that less than 41 million sector writes a year on a 256M Disk in a Routerboard would be no problem at all, provided you wanted a 20 year life before you reached 50% of the write spec of the NAND.
Are those calculations correct?
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