Data storage technology is constantly evolving, and with the release of new software versions such as TrueNAS 25.10 GoldenEye, the question increasingly arises: is it time to replace the well-known iSCSI with the modern NVMe over Fabrics (NVMe-oF)?
Before answering that question, it's worth going back to the origins. iSCSI is a protocol that is more than two decades old. It was created to support disk devices over a network, and for years it worked well - especially in the days when disk drives dominated. Their design enforced sequential data processing: the head could only perform one read or write operation at a time. Thus, all requests went to a single queue, which limited the possibilities of parallel processing.
The situation has changed with the advent of NVMe drives. Unlike classic mechanical drives, they can support multiple queues and perform numerous operations in parallel. It was for them that the NVMe over Fabrics protocol was designed - from the beginning created with multi-threading and maximum performance in mind. Thanks to this, data transmission latency is even several times lower, the number of IOPS operations can double, and the load on the CPU - both on the server and client side - is noticeably reduced.
Does this mean that iSCSI can now be quietly put away? Not necessarily. It all depends on the environment in which we work. For traditional disk drives, the differences will be virtually imperceptible. With an access time of 5 milliseconds, network latency of 0.2 milliseconds is of marginal importance. But with modern NVMe drives, where the access time is just 0.05 milliseconds, every tenth of a millisecond makes a huge difference. Then NVMe-oF can realistically speed up the entire system, even by several times.
The cache is also worth mentioning. In systems like TrueNAS, a large cache hit ratio can make the difference in protocols even with slower drives. If most of the data is read from RAM or from a fast NVMe-based L2 cache, moving to NVMe-oF can yield 10, 20 or even 30 percent performance gains.
However, it is not in every case worth investing in the new technology. To take full advantage of the potential of NVMe over Fabrics, a high-speed network infrastructure is required - preferably at least 25 Gbps. With weaker links, such as 10 or 2.5 Gbps, the gains can be nominal.
By the way, under the term NVMe over Fabrics there are two technologies. The first - NVMe over TCP - runs on a regular IP network and requires no additional hardware outlay, making it an attractive option for those who want to try a new solution without a large investment. The second - NVMe over RDMA - requires special cards and a dedicated network, but in return offers even lower latency and higher performance.
All in all, NVMe over Fabrics is a future technology that can already significantly improve the performance of storage systems, especially those based on NVMe drives and high-speed networks. However, iSCSI remains a solid and proven solution where the priority is not maximum speed, but stability and simplicity. So the choice depends on what your needs are and what kind of infrastructure you have.