6.7

iSER differs from traditional iSCSI as it replaces the TCP/IP data transfer model with the Remote Direct
Memory Access (RDMA) transport. Using the direct data placement technology of the RDMA, the iSER
protocol can transfer data directly between the memory buffers of the ESXi host and storage devices.
This method eliminates unnecessary TCP/IP processing and data coping, and can also reduce latency
and the CPU load on the storage device.
In the iSER environment, iSCSI works exactly as before, but uses an underlying RDMA fabric interface
instead of the TCP/IP-based interface.
Because the iSER protocol preserves the compatibility with iSCSI infrastructure, the process of enabling
iSER on the ESXi host is similar to the iSCSI process. See Configure iSER Adapters.
Establishing iSCSI Connections
In the ESXi context, the term target identifies a single storage unit that your host can access. The terms
storage device and LUN describe a logical volume that represents storage space on a target. Typically,
the terms device and LUN, in the ESXi context, mean a SCSI volume presented to your host from a
storage target and available for formatting.
Different iSCSI storage vendors present storage to hosts in different ways. Some vendors present
multiple LUNs on a single target. Others present multiple targets with one LUN each.
Figure 10‑1. Target Compared to LUN Representations
Storage Array
Target
LUN LUN LUN
Storage Array
Target TargetTarget
LUN LUN LUN
In these examples, three LUNs are available in each of these configurations. In the first case, the host
detects one target but that target has three LUNs that can be used. Each of the LUNs represents
individual storage volume. In the second case, the host detects three different targets, each having one
LUN.
Host-based iSCSI initiators establish connections to each target. Storage systems with a single target
containing multiple LUNs have traffic to all the LUNs on a single connection. With a system that has three
targets with one LUN each, the host uses separate connections to the three LUNs.
This information is useful when you are trying to aggregate storage traffic on multiple connections from
the host with multiple iSCSI adapters. You can set the traffic for one target to a particular adapter, and use
a different adapter for the traffic to another target.
iSCSI Storage System Types
ESXi supports different storage systems and arrays.
vSphere Storage
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