Everyone hates mds_stores, because whilst spotlight can sometimes be handy, actually, no, its never handy and just takes up loads of processor time.

This can be done from the console, so open a terminal window and type:

 sudo mdutil -a -i off

This will disable indexing for all volumes. Theoretically.

Now if your mds_stores is running at 100% and a reboot after the command above doesn't fix it, then you can pull the whole thing. To do this, same terminal type:

 sudo launchctl bootout system/com.apple.metadata.mds.index
 sudo launchctl stop system/com.apple.metadata.mds.index

In a few seconds, your hard disk should return to normal. mds_stores will get started again at next boot, but hopefully it will take heed of the mdutil settings and not thrash your drive.

If you wanted to permanently disable it, you can try :

 sudo launchctl disable system/com.apple.metadata.mds.index

but at the next update it'll probably get re-enabled.

I hope this helps.