Create RAID 1 on new XPS 8100 ?

First, both drives should be the same size.  You can create a RAID only as large as the smaller of the two drives, and once created, any excess space on one of them will be inaccessible.  Your machine appears to have an Intel chipset; Intel based machines use the Intel Rapid Storage application to monitor the drives and allow you to change settings.

To migrate to a RAID:  Once you have installed the second hard drive you should go to system setup, reached by restarting the machine and pressing F2 during the self test.  Use the keyboard arrow keys to navigate to the section for SATA drives to make sure that the new drive is properly registered by the system.  Assuming that the computer sees the new drive, navigate to the SATA controller and make sure that it is set to RAID On.  Allow the computer to boot.  You should see a RAID status screen that tells you the condition of the drives.  After it disappears your computer should boot normally.  After that, go to your programs list and find the Intel Rapid Storage application and bring it up.  At the top of the window that pops up you should see a list of menu items.  I'm still using the older version of this, so what I see under "Actions" is an option to create a RAID from an existing drive.  The help file from my program gives me this:

Follow the steps below to convert the system to a RAID system by migrating data from the existing system drive to a RAID volume.

1. Note the serial number of the hard drive that you want to migrate the data from and ensure that it is connected to the system. You will need the serial number later in the procedure to identify this drive as the source drive.
2. Connect the desired number of additional Serial ATA hard drives to the system to be used as the volume's member drives. Note that these hard drives will need to have a capacity equal to or greater than the capacity of the source hard drive.
3. Start Windows* and open the Intel® Matrix Storage Console.
4. Select 'Advanced Mode' from the 'View' menu.
5. Select 'Create RAID Volume from Existing Hard Drive' from the 'Actions' menu. The 'Create RAID Volume from Existing Hard Drive Wizard' will launch.
6. Follow the instructions throughout the wizard. The migration will begin once the wizard is completed.
7. To view the migration status, right-click on the volume name in the device pane and select 'Show Migration Progress'. A tray icon message will pop up when the migration is complete and the volume's 'Status' will display 'Normal in the information pane.
8. After the migration is complete, restart the system. If you migrated to a RAID 0 volume, use Disk Management from within Windows* to partition and format the empty space created when the two hard drive capacities were combined. You can also use third-party software to extend any existing partitions within the RAID volume.

You should check the help file on your own version of the program to make sure it is at least similar before you actually attempt the operation.  To obtain the serial number of the source drive, which will be your original hard drive, either get it from the system setup list when you check to see if the new drive is recognized, or look at the Rapid Storage window.  Mine lists all drives in use by port and if I click on the drive I get its serial number.

 If you are planning to create a new RAID volume and load everything from DVD/CDs:  With an Intel chipset you generally have the RAID Option ROM.  The setup screen for this is accessed by pressing CTRL i while the RAID status screen is being shown.  You will not see this screen unless the following conditions are met:  The SATA controller must be set to RAID On, and you must have two acceptable drives present in the system.  Using the option ROM screen, however, resets both hard drives to an unused status which will require you to reload everything from scratch and will prevent you from accessing your existing data, at least not without going through a lot of trouble.

Thanks!

I do see the intel App now. Hoping I don't have to re-load everything!

Post back your results.   I have a Sttudio XPS 9100 and was not lucky on doing the coversion to RAID 1.   I bought two disk since I wanted to keep the orginal image around for a while.    I imaged the orginal disk and then replaced the disk with 1 of my new ones.   Booted off the image just made and was able to restore the image to the new disk.    I then installed the second disk made sure it was reconized in the BIOS and then change the type to RAID in the BIOS but the boot up failed.   I tried several thinks and finally created the RAID 1 using the RAID BIOS accessable with CTL I on boot up.   At this point I could of used my image to restore the system but instead decided to reload from scratch.   I was going to use Win 7 Ultimate from the Premium shipped with tne machine.    No issus installing from scratch.    One think that was missing from DELL download was the chip set driver.    I finally found one from Intel for the X55 chip set.

Please post back your results if you could migrated to RAID 1.    I been using RAID 1 for over 7 years and very happy my first dell was a XPS gen2.    I lost several drives on the Gen 2 and XPS 410 and never lost any data.  

OK, new drive arrived today and is identical part number as the one in the 8100. Dumb luck.

Installed in the chassis and was surprised at the new Dell Hard drive mounts. Things are kind of sideways for the HDs but it has space for 2 HDs and I used the empty slot. Disappointed that they didn't put screws and a SATA cable in with the new drive, but I dug around through my old ASUS accessory bag and found the stuff I needed. Buttoned it up and turned it on. Immediately noticed the RAID screen after BIOS and when Windows booted a message appeared in the System Tray telling me the new driver for the HD had been installed successfully.

I shut down and restarted with an "F2" to enter BIOS and reviewed settings. RAID was on for the SATA controller and the second disk was seen on port 3. Original HD on Port 0. Exited BIOS without saving and allowed system to boot. Got another message in the System Tray that Intel Rapid Storage Technology had detected another drive and it could be used to enhance the system by clicking the balloon. I clicked. It opens Intel  program at "Status" and asks if i want to create a volume for Protection or custom. I choose protection and go through the steps until I get an error message that it can't create the volume.

So I choose "Custom". Then choose the master HD and RAID 1 config. It starts creats the Volume and starts migrating Data. about 3% complete as I type.

This was too easy. I will post back here later when it is completed. Seems like a really good program with an in depth Help file from Intel.

Thank you both for your guidance.

Seems to be successful.

It did take a very long time to migrate the data, but the drives are 1.5 TB , after all. I would estimate about 8 hours, although at some time during the night , a power management feature must have hibernated the machine. No matter as it picked right back up and completed the migration. It is curious that it seems to make no difference that there was very little data on the master drive. Just OS and Office install. Apparently the RAID process must mirror the two drives sector by sector regardless.

Re-booted and received a message that a driver had been installed and windows needed to restart, so I did.

Very painless and did I mention this seems too easy?

I'm very glad that everything is working out well.  Best of luck to you!