iPod Classic failure?

I'm synchronizing my 160GB iPod Classic (Built 2011) and during the first minutes copies around 400 songs (I'm copying a playlist which has plus than 8000 songs) but then it slows down and copies each song on a minute (In 1 hour only transfered 1189-1206 songs, still transferring) Could the disk be damaged? One thing to notice is that I've tried to sync it up before (Just one time) and then disconnected the iPod. When I plugged it back a message popped up on iTunes: Something about the hard drive being corrupted and the need of doing a restoration. So I did. What's wrong? Is the HD failing? Could I try to fix it for myself (Using the iPod or my mac)?

For the record: I have another 160GB Classic (Built 2012) and it gives me no trouble. Sync is fast compared to this one.

Any help would be appreciated.