Fibre Channel and iSCSI comparison for MSDP
Deduplication is a CPU and memory intensive process. It also requires dedicated and high-speed storage connectivity for the best performance. That connectivity helps to ensure the following:
Consistent storage performance.
Reduced packet loss during network congestion.
Reduced storage deadlocks.
The following table compares both the Fibre Channel and the iSCSI characteristics that affect deduplication storage performance. By design, Fibre Channel provides the greatest opportunity to meet performance objectives. To achieve the results that are required for NetBackup MSDP storage, iSCSI may require other optimizations that are described in the following table.
Table: Fibre Channel and iSCSI characteristics
| Item | Fibre Channel | iSCSI |
|---|---|---|
|
Genesis |
Storage networking architecture that is designed to handle the same block storage format that storage devices use. |
Storage network protocol that is built on top of TCP/IP to use the same wiring as the rest of the enterprise. |
|
Protocol |
FCP is a thin, single-purpose protocol that provides lossless, in-order frame delivery and low switch latency. |
iSCSI is a multiple layer implementation that facilitates data transfers over intranets and long distances. The SCSI protocol expects lossless, in-order delivery, but iSCSI uses TCP/IP, which experiences packet loss and out-of-order delivery. |
|
Host CPU load |
Low. Fibre Channel frame processing is offloaded to dedicated low-latency HBAs. |
Higher. Most iSCSI implementations use the host processor to create, send, and interpret storage commands. Therefore, Veritas requires dedicated network interfaces on the storage server to reduce storage server load and reduce latency. |
|
Latency |
Low. |
Higher. |
|
Flow control |
A built-in flow control mechanism that ensures data is sent to a device when it is ready to accept it. |
No built-in flow control. Veritas recommends that you use the Ethernet priority-based flow control as defined in the IEEE 802.1Qbb standard. |
|
Deployment |
Difficult. |
Easier than Fibre Channel, but more difficult to deploy to meet the criteria for MSDP. The required dedicated network interfaces add to deployment difficult. Other optimizations for carrying storage traffic also add to deployment difficult. Other optimizations include flow control, jumbo framing, and multi-path I/O. |
Although Veritas supports iSCSI for connectivity to storage, Veritas recommends Fibre Channel. Veritas believes that Fibre Channel provides better performance and stability than iSCSI. iSCSI instability may manifest as status 83 and status 84 error messages.