VMFS vs. RDM – Fight!

VMFS vs. RDM – Fight! [vsphere-land.com]

VMFS vs. RDM – Fight!

The question often comes up, when should I use Raw Device Mappings (RDMs) instead of traditional VMFS/VMDK virtual disks. The answer for this usually is, always use VMFS unless you fit into specific use cases. An RDM is raw LUN that is presented directly to a VM instead of creating a traditional virtual disk on a VMFS datastore. Because a VM is directly accessing a LUN there is a natural tendency to think that a RDM would provide better performance as a VM is reading/writing directly to a LUN and not having to deal with the overhead of the VMFS file system. While you might think that, it’s not the case, RDM’s provide the same performance levels as a VM on VMFS does. To prove this VMware performed testing and published a white paper way…Read More


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