In this article, we will take a closer look at the iSER technology. It stands for iSCSI extensions implemented with RDMA. Generally, this technology extends the functionality of the iSCSI protocol by adding RDMA support, lowering the utilization of the CPU as well as decreasing the latency.

With iSER, you are using the good old iSCSI but with a few differences. iSER setups utilize the same software as iSCSI, so the same initiator and target are used. All you would need to do is configure the initiator side to use the iSER interface when performing iSCSI discovery. As far as you can see, it's as simple as it gets to improve your overall storage performance.

Before we get into all the details, I would like to mention the overall benefit of the iSER implementation. The improvement of performance is achieved in a way that the amount of read/write operations is issued by RDMA instead of the CPU, resulting in the load reduction on the CPU.

 

While utilizing the existing iSCSI mechanism, the iSER protocol is capable of determining if it should use iSER or iSCSI data transfer models. The network cards with their hardware offload support take advantage of this efficient RDMA transport service over Ethernet to deliver ultra-low latency for performance-critical and transaction-intensive applications, such as financial, database, storage, and content delivery networks. In the case of RDMA over Converged Ethernet (RoCE), it would be possible to eliminate the TCP layer completely.

Taking into account that iSER is much easier to manage than iSCSI, it is also capable of providing much higher bandwidth for block storage transfers. Due to all its performance advantages, it remains stable and can provide both security and high availability of iSCSI at the same time.

As you can see, the difference in performance between IP-based iSCSI and RDMA-based iSCSI over Ethernet is huge. Other than the requirement of specific Ethernet adapters/switches, there is really nothing else holding you back from accelerating the storage.

In the process of choosing RDMA over Ethernet, it would be a great idea to double check that the switch vendor can guarantee compatibility of the RDMA requirements with the adapters you plan on using when building the network. It becomes clear that iSER is a great technology in many use cases.