Actually....that is the backup copy of your MFT (master file table). That is there in case something happens to the first (primary) MFT. Provided of course you are using the ntfs file system. (w/ 2k/nt/xp windows systems). It is nothing to be worried about. If it disappears for some reason, then you have a problem.
Remember reformating is the last option. Try everything before you do it. Also remember to make backups, I once reformatted without backing anything up and lost $400 dollars worth of programs and over 200+ renders.