| Do you really need an iSCSI host bus adapter (iSCSI | | | | handle iSCSI packets until it is up and running, an |
| HBA)? The short answer is no, with a but. It is | | | | iSCSI SAN without an HBA must boot from a directly |
| possible to build a working iSCSI SAN with all of it | | | | attached hard drive or other device. |
| features using standard Ethernet network interface | | | | However, there are now ways to boot from an |
| cards (NICs) as the initiators, but it might not be the | | | | iSCSI SAN without HBAs. For example, NetBoot |
| best plan to have an iSCSI SAN with out an iSCSI | | | | software from iSCSI HBAenables booting by storing |
| HBA | | | | a copy of the system's boot volume in the iSCSI |
| Older versions and models of iSCSI SAN’s | | | | array and using a Windows boot initiator on the |
| needed iSCSI HBA’s because the SAN’s | | | | system driver to load the boot files from the SAN at |
| would perform poorly without iSCSI HBA’s. The | | | | startup. |
| two issues with iSCSI SAN’s that do not use | | | | There is one last factor to consider. Originally, most |
| HBA’s are performance and booting. | | | | iSCSI SAN’s were alternatives to, or |
| One big variation between an iSCSI HBA and a | | | | replacements for, Fibre Channel SAN’s. They |
| conventional NIC is that the HBA includes a TCP | | | | were not expected to offer the same performance |
| Offload Engine (TOE), which is an support processor | | | | as FC SAN’s -- early iSCSI SAN’s didn't have |
| that takes care of wrapping and unwrapping SCSI | | | | the same throughput as FC SAN’s and even |
| information in Ethernet frames. Since handling iSCSI | | | | today a high-performance SAN is more than likely an |
| maintenance can easily eat 20 percent or more of | | | | FC SAN. |
| the CPU cycles of the iSCSI server, the server in an | | | | However, the low cost of iSCSI SAN’s is |
| iSCSI SAN that does not use an iSCSI HBAmay show | | | | increasingly encouraging enterprises to use them in |
| a loss in performance. | | | | areas that do not require the performance of an |
| Nevertheless, the trend toward increasingly powerful | | | | enterprise SAN, such as snapshotting or for |
| servers at reduced costs means that more servers | | | | departmental computing. |
| are likely to have the CPU cycles to spare. This is | | | | Conclusion: In some instances it is worth considering |
| especially true in environments that do not virtualize | | | | an iSCSI SAN without an iSCSI HBA. But it will take |
| their servers. | | | | analysis, and probably some testing with performance |
| In relation to boot issue, an HBA initiator lets the | | | | tuning tools such as iostat, to see if you can get by |
| system boot from the SAN. Since the system can't | | | | without iSCSI HBA’s in a particular application. |