How Do I Partition A Raid 0 Using Disk Utility? I have just purchased a WD My Passport Pro. It comes in a striped RAID 0 configuration comprising of two 2TB drives.

I want to partition the drive into 3:


Photoshop Cache
Lightroom Catalogue
Video files


I am not worried about backup as I am backing up regularly from this RAID.

When I look at the drive in Disk Utility there is no tab for partitioning, so I am unable to create there partitions. How can I do so?
Things to check for. Some Raid devices are set/Fixed for only one type of Raid 0 or 1. You should check the box and see if this can be used for anything other than Raid 1. Also there maybe software from WD on the drive that will change the Raid for you. If the WD is not hardware locked to be only a Raid 1 and you are unable to find WD software you can try the steps below. 
If you can not erase the WD with Disk Utility then try looking over instructions to erase it from the command line on this site. 
http://www.theinstructional.com/guides/disk-management-from-the-command-line-part-1

We will do this in three steps. 


Erase
Create the Raid
Partition the Raid


The hard drives you will be using as members of the RAID 0 striped set must first be erased. And since a RAID 0 set can be severely impacted by a drive failure, we’re going to take a little extra time and use one of Disk Utility’s security options, Zero Out Data, when we erase each hard drive.

When you zero out data, you force the hard drive to check for bad data blocks during the erasure process, and mark any bad blocks as not to be used. This decreases the likelihood of losing data due to a failing block on the hard drive. It also significantly increases the amount of time it takes to erase the drives from a few minutes to an hour or more per drive.

Erase the Drives Using the Zero Out Data Option

Make sure the hard drives you intend to use are connected to your Mac and powered up.
Launch Disk Utility, located at /Applications/Utilities/.
Select one of the hard drives you will be using in your RAID 0 striped set from the list on the left. Be sure to select the drive, not the volume name that appears indented under the drive’s name.
Click the ‘Erase’ tab.
From the Volume Format dropdown menu, select ‘Mac OS X Extended (Journaled)’ as the format to use.
Enter a name for the volume; I’m using StripeSlice1 for this example.
Click the ‘Security Options’ button.
Select the ‘Zero Out Data’ security option, and then click OK.
Click the ‘Erase’ button.
Repeat steps 3-9 for each additional hard drive that will be part of the RAID 0 striped set. Be sure to give each hard drive a unique name.
Now that we have erased the drives we will use for the RAID 0 striped set, we’re ready to start building the striped set.

Create the RAID 0 Striped Set


Launch Disk Utility, located at /Applications/Utilities/, if the application is not already open.
Select one of the hard drives you will be using in the RAID 0 striped set from the Drive/Volume list in the left pane of the Disk Utility window.
Click the ‘RAID’ tab.
Enter a name for the RAID 0 striped set. This is the name that will display on the desktop. Since I will be using my RAID 0 striped set for video editing, I’m calling mine VEdit, but any name will do.
Select ‘Mac OS Extended (Journaled)’ from the Volume Format dropdown menu.
Select ‘Striped RAID Set’ as the RAID type.
Click the ‘Options’ button.
Set the RAID Block Size. The block size is dependent on the type of data you will be storing on the RAID 0 striped set. For general use, I suggest 32K as the block size. If you will be storing mostly large files, consider a larger block size, such as 256K, to optimize the performance of the RAID.
Make your choices on the options and click OK.
Click the ‘+’ (plus) button to add the RAID 0 striped set to the list of RAID arrays.


With the RAID 0 striped set now available in the list of RAID arrays, it’s time to add members or slices to the set.

Add Slices to Your RAID 0 Striped Set


Drag one of the hard drives from the left-hand pane of Disk Utility onto the RAID array name you created in the last step.
Repeat the above step for each hard drive you wish to add to your RAID 0 striped set. A minimum of two slices, or hard drives, is required for a striped RAID. Adding more than two will further increase performance.
Once you add all of the hard drives to the RAID 0 striped set, you are ready to create the finished RAID volume for your Mac to use.
Click the ‘Create’ button.
A ‘Creating RAID’ warning sheet will drop down, reminding you that all data on the drives that make up the RAID array will be erased. Click ‘Create’ to continue.
During the creation of the RAID 0 striped set, Disk Utility will rename the individual volumes that make up the RAID set to RAID Slice; it will then create the actual RAID 0 striped set and mount it as a normal hard drive volume on your Mac’s desktop.
The total capacity of the RAID 0 striped set you create will be equal to the combined total space offered by all members of the set, minus some overhead for the RAID boot files and data structure.
You can now close Disk Utility and use your RAID 0 striped set as if it were any other disk volume on your Mac.