Q: What's iSCSI direct?

A: iSCSI direct is a term that's commonly associated with iSCSI connections that are directly attached into Hyper-V virtual machines (VMs). Hyper-V supports the ability to create an iSCSI connection at the host and then associate that connection with a VM. This creation of the iSCSI connection at the host is called a pass-through disk.

Microsoft asserts that pass-through disks experience performance that is roughly equal to native connections. Pass-through disks, however, require additional configuration and participation from the Hyper-V host.

With iSCSI direct, the iSCSI connection goes directly to the VM instead. This simplifies the configuration and eliminates the participation of the host. They're easier to configure and manage than pass-through disks, but iSCSI direct connections suffer a small reduction in performance compared to pass-through.