Due to the architecture of PowerEdge 2950, we will not be able to disable the RAID configuration. But there is configuration step that you can use, RAID0 using only 1 HDD in 1 array (Assuming you are using a PERC5i in a PE2950). Get what i meant?
Once installed ESXi on this 2950, mentioned that you are going to import the 2 other disk from other servers, are the servers also 2950? Are they in RAID too? Reason that I asked, is that if the 2 disks are in RAID and also from a 2950, you will need to import foreign configuration in the RAID BIOS.
The reason ESXi 5.1 installation doesnot see the disks, RAID driver is not loaded in ESXi installation CD. Here's the OEM version from Dell: http://dell.to/1a32bXk
Answer to the last question, the added other disks will need to be formatted
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