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VMware ESX and ESXi Server
VMware ESX and ESXi Server
| Adding a raw device mapping (RDM) to a virtual machine |
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A Raw Disk Mapping (RDM) may be used to present a LUN directly to a virtual machine from the SAN. This offers improved performance, which can be used for more disk IO intensive applications such as database servers.
The first step to adding a RDM to a virtual machine is to assign an unused LUN to your ESX/ESXi Server(s). This will vary depending on the type of SAN in use.
For the new LUN to become available, Rescan the HBAs on all your ESX servers.
 The virtual machine that the RDM is going to be added to needs to be shut down first, the RDM cannot be added while it is running.
Once the VM is shutdown right click the VM and choose "Edit settings".
On the hardware tab, click "Add" and choose "Hard Disk".
For the disk type choose "Raw Device Mapping" (RDM). Click Next.
 Choose the LUN. Click Next.
 Choose "Store with virtual machine" or if you want store the link to the RDM in a specific datastore. Click Next.
 Choose "Physical" or "Virtual" compatability. Click Next.
 The RDM needs to be on a seperate SCSI controller. Choose a Virtual Device Node that is on a different SCSI bus to the current virtual disks (e.g. SCSI 1:0). Click next.
 Confirm settings and choose finish.
 A new SCSI controller and hard disk is added to the virtual machine configuration. Now boot your VM. Depending on the OS check for new disks and format/mount the disk.
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