It's the battle of the century. In one corner, promoted by every major server and storage vendor, is Fibre Channel....
In the other corner, promoted primarily by NAS vendors, startups and users, is iSCSI. Have you had enough of the hype?
These two SAN technologies have been positioned as fierce competitors. However, major server and storage vendors don't necessarily see it as Fibre Channel vs. iSCSI; most popular SAN arrays support both FC and Ethernet instead of being designated as FC SANs or iSCSI SANs.
Both iSCSI and FC technologies solve the same technical problem of networking block storage. The differences between the two configurations are in the details. There are five areas to consider when picking a SAN technology:
- performance and reliability
- complexity and ease of use
- total storage SAN solution
What follows is a look at the Fibre Channel vs. iSCSI debate, how each technology works and how they compare in the five areas outlined above.
Fibre Channel explained
FC is a high-speed networking technology. It typically has throughput speeds of 8 Gbps, 16 Gbps and 32 Gbps but can go up to 128 Gbps by combining four 32 Gb lanes. It was originally designed for use in SANs as a more reliable, scalable and lower-latency protocol than SCSI. Today, its use is driven by the increasing data volumes businesses generate through the use of analytics, AI and machine learning technologies, as well as the growing use of SSDs and NVMe-oF to improve application and network performance.
Connecting servers with shared storage and providing connectivity between storage controllers and drives are the main ways FC is used. It's often used to transmit data among data centers, servers, storage and switches. Point-to-point, switched and loop interfaces deliver lossless, in-order, raw block data. FC networks are designed to interoperate with SCSI, IP and other protocols.
Because of its high level of reliability, FC is preferred for mission-critical workloads on high-capacity SANs. However, FC requires specialized adapters and switches, as well as extensive technical knowledge and skills to deploy the technology. In addition, businesses generally need two networks when using an FC SAN: the FC network for storage traffic and an Ethernet network for other communication and bandwidth.
ISCSI is an Ethernet-based protocol designed to transport SCSI packets over a TCP/IP network. Because it uses standard Ethernet network interface cards and switches, network admins don't need to buy the specialized adapters and network cards that add to the expense and complexity of FC SAN technology. ISCSI can run over an existing Ethernet network, also making it less expensive and easier to deploy than FC.
An iSCSI network can run at speeds up to 100 Gbps. It transports block-level data between servers and storage arrays or other storage devices. The protocol encapsulates SCSI commands, assembles the data in packets for the TCP/IP layer and sends packets over the network using a point-to-point connection. Once at their destination, the packets are disassembled, and the storage appears to the OS as if it is a locally connected SCSI device.
Fibre Channel vs. iSCSI performance
Fibre Channel is a layer 2 switching technology or cut through, with the protocol handled entirely in hardware. The iSCSI protocol (SCSI mapped to TCP/IP) running on Ethernet is a layer 3 switching technology with the protocol handled in software, hardware or some combination of the two.
FC is often touted as the high-performance, more reliable SAN technology. Early in iSCSI development, that was true, but that's not the case anymore.
Today, performance bottlenecks are far more likely to be the result of the target storage (interface, controller queue depth, controller clustering, number of disks, disk type, etc.), the physical server or the SAN fabric oversubscription rate (number of server initiators to number of storage target ports) than the SAN technology.
So, which technology is the better performer? All things being equal, FC should be marginally better in IOPS (because of lower latency) and throughput (because of lower overhead).
Complexity/ease of use
Because the iSCSI SAN is based on the well-known TCP/IP and Ethernet, it's far simpler and less complex than FC. The learning curve and expertise requirement for FC is measurably higher. FC tends to be significantly more manually intensive vs. iSCSI, which has a lot more built-in automation. As a result, FC technology usually requires more training, a greater knowledge base and ultimately higher costs with both.
When it comes to Fibre Channel vs. iSCSI, hands down, iSCSI SANs are far easier to implement, operate and manage than FC. ISCSI uses the vast capabilities of TCP/IP and Ethernet and is much less expensive. Most moves and changes are performed online and aren't disruptive to applications.
Although FC has come a long way in manageability, the majority of moves and changes are application-disruptive. This means they must be scheduled and performed offline. The alternative is to live with the application disruptions and, in some cases, deal with potential data loss.
Total SAN solution and TCO
When considering the total SAN approach in the Fibre Channel vs. iSCSI debate, the assessment must involve the complete end-to-end package, including the storage system, the storage software (snapshot, mirroring, thin provisioning, etc.) and the types of drives (solid-state flash vs. HDDs).
When assessing TCO, make sure to include the acquisition, installation, professional services (if any), additions and upgrade, management, operational, maintenance, subscription, power, cooling and real estate costs. These costs apply to the storage system, the SAN and the storage software.
FC vendors have done a good job in reducing the costs of their products. But these products have a considerably higher TCO than the iSCSI equivalents. The adapters, switches -- especially the data center class switches called directors -- and software all have considerably higher TCO than their iSCSI equivalents.
Bottom line: How do you make the Fibre Channel vs. iSCSI decision for your SAN? The answer is: It all depends. Choose the technology that best meets your requirements for performance, ease of use, manageability, total package and TCO.
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