Second disk offline during deployment

Yesterday I did an deployment on a virtual server with 2 disks. During WinPE phase I checked diskpart (in a command window) and both disks were online. However after the "Setup Windows and ConfigMgr" step and reboot to Windows, the second disk went offline. Because of multiple tasks on the second drive, the task sequence was failing. Let's use diskpart to change the second disk to online mode again.

WinPE Phase (boot image)

Windows Phase before diskpart

Open Notepad an paste the following lines:
select disk <?>
online disk
attribute disk clear readonly

Replace <?> with the disk number of the disk (without the brackets <>). Save the Notepad file with the name diskpart.txt (for example). In the ConfigMgr console create a new package (without a program) with the txt file in it.

During the task sequence, immediately after the "Setup Windows and ConfigMgr" step, add a "Run Command Line" step with the command: "diskpart /s diskpart.txt" and use the package created before.

Windows Phase after diskpart

After that the disk will be online again. Hope it helps!

Source: Microsoft TechNet