Virtualized Exchange Storage: VMDK or RDM or…?

#Exchange #Exchange2010 #vmware

Matt sent me this .. an Interesting read

http://blogs.vmware.com/apps/2011/11/virtualized-exchange-storage-vmdk-or-rdm-or.html

One of the hottest topics I get into when talking to customers about virtualizing Exchange is storage. Not surprising considering the number of options available when we virtualize Exchange on vSphere. If you are not familiar with the common methods for provisioning storage in vSphere a brief description of each follows:

  • VMFS based virtual disk (VMDK) – VMFS is a high performance, clustered file system that allows concurrent access by multiple hosts to files on a shared volume. VMFS offers high I/O capabilities for virtual machines and is optimized for large VMDK files. VMFS volumes can be Fibre Channel or iSCSI attached.
  • Raw-device mappings (RDM) – RDM is a mapping file in a VMFS volume that acts as a proxy for a raw physical device, sometimes called a pass-thru disk. The RDM file contains metadata used to manage and redirect disk access to the physical device. RDMs can be Fibre Channel or iSCSI attached.

In early versions of ESX the virtualization overhead associated with deploying virtual disks (VMDK files) was much higher than it is today and why it was considered a best practice to place Exchange data files on physical mode raw-device mappings (RDM). As ESX and vSphere have evolved the performance difference between RDMs and virtual disks has become almost nonexistent. This leaves some questioning why we might choose to deploy RDMs for Exchange storage.

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