mkdosfs - with bad blocks - why does it slow down near the end?

Question

I'm attempting to fix an ipod that has bad sectors - its 'surplus' and a search for spares locally proved futile. I'm convinced it is age related, so i'm trying use mkdosfs with the -c option on it, to create a new filesystem with the bad blocks marked off. While the initial stages of the scan are fast - roughly 10K of whatever arbitrary unit they use per update, down to to about 5 every update.

I'm wondering why this is - is it something to do with the error, or something interistic to the drive

Answer 1

I'm doing exactly the same: trying to format an ipod classic with a HDD apparently full of bad blocks.. It takes long because the bad block test consist of writing some data to the block being tested and then read it right away. If the data read differs from the data written, it tries again. write & read, and again, before marking that block as bad. That delays the process a lot.