Hi! > > > - Similarly, there is a small chance that chkdsk on Windows will > > > rename one file in a directory if they happen to have the same 11 > > > byte dummy values. The probability of this happening is > > > approximately 80x lower than with the previous patch. > > > > The "small chance" seems to be 90% for 30000 files in directory. And > > no, it is probably not 80x lower. Do the math. > > Perhaps you could double check my math? > > The number of combinations available with the current patch is > 35^6 * 7 * 8 for files (for directories there are more combinations, > but lets ignore that for now). > > That comes to 102942875000 combinations. > > Now we can do the exponential birthday approximation, which is: > > p = 1.0 - exp(-(n * (n-1)) / (2 * m)) > > where n is the number of entries in the directory, and m is the total > number of combinations. > > That comes to about 0.0052 for 32767 files in a directory > (ie. maximully full), or about 0.5%. > > With the previous patch we had 2^30 combinations, which came to 0.393, > or about 39%. So the new patch has about 75x lower chance of a single > collision than the old one. > > Similarly for 100 files, the old patch gave a probability of > 4.6*10^-6, whereas the new one gives 4.8x10^-8, which is about 96x > lower chance of a single collision. I guess I should apologize here. I did not do the math. It just seemed to me that from the paradox of twins, difference should be greater. Sorry for confusion. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
