RDM disks for VMware vSphere VMs: how & why to create them

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.

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Testing iSER on ESXi

VMware ESXi is the industry-leading hypervisor that is installed directly on a physical server. It is a reliable and secure solution with a tiny hardware footprint. At the same time, ESXi architecture is easy in management, patching, and updating.

Recently, Mellanox has released iSER, the stable iSER driver build for ESXi. iSER is an iSCSI extension for RDMA that enables the direct data transfer out and into SCSI memory without any intermediate data copies. Here, we study the driver stability and performance to understand how the protocol streamlines ESXi environments.


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