Today, of course, virtualized infrastructure doesn’t sound as ludicrous as it would have been decades ago, but it cannot be precisely said that it has become common. Virtual SANs, for example, are known for being efficient and handy analogs of cumbersome SANs, but what we really know about their performance, how can it be different at times, and why?”
Sometimes, you need your VMs to access a LUN directly over iSCSI. Direct access comes in handy when you, let’s say, run SAN/NAS-aware applications on vSphere VMs, or if you’re going to deploy some hardware-specific SCSI commands. Also, with direct access, physical-to-virtual conversion becomes possible without migrating a massive LUN to VMDK. Whatever. To enable your VMs to talk directly to LUN, you need a raw device mapping file. Recently, I created vSphere VMs with such disks. Well, apparently, this case is not unique, so I decided to share my experience in today’s article.