create new start up on ext drive

Hi I use drive genius to monitor my computer and lately it informs that there are errors that need repairing,I have gone to disc utility to verify preferences and then repaired preferences but I still get the same warning. so I thought I could use my(porsche 9230 Lacie) as a start up.I tried to set up a new partition to name as ext start up but it tells me I will wipe my ext drive and I will lose all data.I already use as my time machine so I'm worried that I am doing the right thing . Anyone got any advice?

Without giving us any information about your computer, how can we advise you? Year? Model? Version of OS X? Post back that info and then we'll offer some solutions.

In order to save your data on the ext drive and use it as a start up disk you will need to add a new partition . This will isolate your existing data and allow you to boot from the 2nd partition.

in disk utility
select the hard drive you want to add a partition to. You need to select the hard drive in the left hand pane not the existing partition
Down under the little image of the drive click the + then select the size you want it to be
then name it and then click apply
This will not erase the data from the first partition
Now when you go to install the OSX select the second partition from the list of drives to install to