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Fibre Channel (FC) connection to storage, it had long seemed to me, was holding on in enterprises in which a big investment in it had been made—but was, overall, in a slow but ultimately terminal decline. The younger upstart iSCSI (usually over Ethernet) was gaining market share, especially in smaller organisations, and had leap-frogged FC speeds. 16Gb FC has helped modify my perception.
In late May Infortrend released the world’s first 16Gb FC storage solutions implementation, built on its EonStor DS G7i RAID platform. This was not merely to match the now established iSCSI transmission speeds (commonly 10GbE) by doubling the previous 8Gb limit (with backwards compatibility to support 4 and 8Gb), but was also aimed at attracting some SMEs who had not looked at FC before.
In mid-June, Infortrend announced that Emulex LightPulse 16Gb FC Host Bus Adapters (HBAs) (the LPe 16000B) had been certified for its DS G7i storage solutions, fully tested for compatibility and performance in an end-to-end 16GFC Storage Area Network (SAN) solution.
Somewhat earlier, Storage Magazine awarded the QLogic FlexSuite 2600 Series 16Gb FC adapter the gold cup and 2012 product of the year in its networking equipment category (the only product presented with an award in fact). Not only is this again backwards-compatible to support 4 and 8Gb FC, it can also be transformed by a field-programmable firmware upgrade into its 8300 Series converged network adapter (CNA) to support 10GbE networks and FC over Ethernet (FCoE).
CNA cards are becoming ever more common for companies wishing to hedge their bets for the future. These developments mean that there is, seemingly, less concern to rush to iSCSI. FC cabling is now also widespread so is less of a constraint (while FCoE is there as a last resort option if fibre optic cabling is replaced by Ethernet to standardise enterprise cabling).
Then let’s throw in FC over IP (FCoIP or FCIP), which is used primarily for linking FC SANs. FCIP transparently interconnects FC SAN islands over IP networks, encapsulating the FC frames so that both SCSI and non-SCSI frames can be transported. So iSCSI allows IP-connected hosts to access iSCSI or FC-connected storage. This combination can be used for FC I-O communication and for remote backup and replication.
All in all, the arguments in favour of either iSCSI or FC seem to be diminishing. Data transmission speeds over either FC or iSCSI over fibre optic cabling can be very similar (albeit this varies according to the mix of data transmitted) and there is nowadays comparatively little difference between FC, FCoE and iSCSI in provisioning, installation and support complexity.
FC and iSCSI administration approaches are, though, different. FC is a centrally managed network-centric protocol, the network controlling what each end device can access; it requires some FC skills to administer and is best for controlling access to a pool of shared storage. iSCSI is end node-centric with the network allowing communication between the iSCSI ‘Initiator’ and ‘Target’ devices; this needs no special SAN administrator skills. Conversely, while this is easier for SMEs to move to comparatively simple SANs, the end devices only discover what the administrator points them to discover, and this can become more complex as the SAN grows. LUN masking implementation is needed either way, and this also forces some centralised control of storage resources.
Arguments over whether FC is more reliable than iSCSI or vice-versa and in what situations – especially at the highest transmission speeds – may never be resolved. There is no practical distance limit for remote transmission over Ethernet (except for potentially unacceptable response delays), but even the limits on FC distances are diminishing; high-quality dark fibre optic cable can accommodate a 250-mile limit with a 2.5ms response time, and such cabling is becoming more common.
So, now, there may often be little to choose between FC and iSCSI. It will instead be what makes most sense for each specific business. The situation is anyway evolving all the time – and other new protocols may yet emerge that start to eat into both standards’ market shares. It’s a safe bet FC will be with us for a long time yet.