External hdd as RAID Concatenated Disk?

[EvanLugh]

I'm following a tutorial to add my External hdd to add ontop of my Mac's hard drive.

iewer for Disk Utility:
Select one of the disks that you want in the set, and then click RAID.
Click Add (+), and type a name for the RAID set.
Choose a format from the Volume Format pop-up menu. Usually you’ll choose the Mac OS Extended (Journaled) format.
Choose Concatenated Disk Set from the RAID Type pop-up menu.
Drag the disks you want to use to the set.
Click Create.

Unfortunatly, i cannot click 'create' as it's blanked out. Any ideas?
Thanks.

 

[blodwyn]

I'm following a tutorial to add my External hdd to add ontop of my Mac's hard drive.


Unfortunatly, i cannot click 'create' as it's blanked out. Any ideas?
Thanks.

You're out of luck if you're trying to create a RAID set using the disk you're currently booted from. You can only create a RAID set from other mounted volumes. One way to achieve what you want is to:

1) Clone your internal Mac boot disk to another disk and boot from it
2) Create a RAID set using your internal Mac disk and the external
3 Clone the disk you're booted from onto the RAID set
4) Reboot from the RAID set

 

[EvanLugh]

I was doing it from the external. Therefore doubling the amount of space 'on my mac'.

 

[blodwyn]

I was doing it from the external. Therefore doubling the amount of space 'on my mac'.

Maybe I'm misunderstanding, but you need 3 disks to do what you're attempting. One disk to boot from, and two additional disks to create the RAID with

Also be aware that if you're concatenating the internal and external to make a single larger volume, that a failure in either drive will be fatal to the volume. So you're roughly doubling the risk of losing your data (assuming similar MTBF for both the disks) and therefore making a backup strategy even more important.