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Home > Host bus adapter upgrades and replacements |
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| SAN Expansion Best Practices: |
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Even though HBAs are not frequently updated, there are some circumstances when HBAs must be changed. Two common reasons for upgrading HBAs are to get faster connectivity or to add ports for aggregation or failover. Other reasons to change HBAs may include better reliability, more stable or mature drivers and management software, superior RAID and virtualization support. This section of the guide highlights some best practices and goals for HBA expansion or replacement. Best Practice No. 1: Don't overbuy HBAs Storage architects and administrators have the least control over HBA selection and implementation. HBAs are normally purchased as part of a new server with an understanding of the switches and other SAN infrastructure that will be in place. Consequently, it's poor practice to overbuy an HBA during an initial purchase unless other SAN expansion plans are already in place. There is no reason to purchase HBAs with 4 Gbps connectivity if the SAN speed is not expected to evolve beyond 2 Gbps. Similarly, there's no reason to buy more HBA ports than necessary unless you plan to implement port aggregation or failover schemes. Best Practice No. 2: Standardize on a primary HBA vendor Storage administrators can reduce potential interoperability problems with HBAs by relying on vendor compatibility matrices and using the same HBAs whenever possible. This will also reduce the amount of maintenance needed for firmware updates. However, it's also a good practice to qualify HBAs from a second vendor in the lab, so an alternate HBA can be used in cases where the original vendor's HBA is unavailable or has changed in an unexpected way that introduces interoperability or performance issues in your environment. Best Practice No. 3: Eliminate bottlenecks in the HBA itself Select an HBA that provides local processing electronics that are dedicated to each port. This practice eliminates HBA ports "sharing" the same chip and forming potential bottlenecks for network data. This improves performance in the HBA and reduces common failures. For example, if four ports are serviced by the same chip and that chip fails, all four ports can be disabled. However, if a chip only drives one port and that chip fails, only that port is affected, improving overall availability and reliability on the SAN. "The mere presence of ports on an adapter doesn't necessarily mean more performance," says Greg Schulz, founder and senior analyst at the StorageIO Group. It is important to select a host bus (e.g. PCI, PCIe or PCI-X) with enough bandwidth to support all of the port traffic that you expect to handle. Today, PCIe is the fastest readily available PC-based bus, offering a maximum theoretical data transfer rate of 8 GBps between expansion cards and the computer backplane. By comparison, the PCI-X supports data transfers to 1,064 MBps, while the antiquated PCI bus tops out at 532 MBps. Best Practice No. 4: Use multiple HBAs for superior availability A single HBA may provide adequate performance when connecting a host server and SAN, but it can present a single point of failure that is an unacceptable practice for reliable SAN design. Experts note that using a single adapter and allowing failover to another SAN cluster is also a poor design choice. Schulz notes that it's equally bad practice to connect multiple HBA ports to the same switch or even to interconnect the switches. "Keep your separate paths," he says. "Don't mistakenly create one single fabric by interconnecting the different devices." Best Practice No. 5: Test new drivers and firmware before deployment HBA drivers and firmware are updated periodically. Unfortunately, system administrators and IT technicians often make updates without first establishing their stability and performance. New does not always mean better, and there are circumstances when a new HBA driver or firmware version can actually impair SAN performance. It's certainly important to identify new drivers and firmware updates, but make it a point to test those updates carefully in a lab environment. Consider any differences in interoperability, performance and stability, quantify any differences, if possible, and then decide whether to roll out the updates to the corresponding HBAs in your environment. Best Practice No. 6: Embrace NPIV for virtualization N_Port ID virtualization (NPIV) allows a physical HBA port to be partitioned to support multiple virtual machines, enabling multiple virtual fabrics through the same physical HBAs and switches. It's not an essential feature for nonvirtualized environments. However, with many organizations moving aggressively toward server and storage virtualization, future HBA upgrades may require features like NPIV. However, experts note that NPIV does not directly support VMware's file system at this time, though this should change as NPIV development continues. Best Practice No. 7: Look ahead to FCoE The storage industry leaders have recently started an initiative intended to combine network protocols, dubbed Fibre Channel over Ethernet (FCoE). This new layer 2 networking standard allows Fibre Channel information to reside within the data payload of Ethernet packets. If successful, this new standard should merge Fibre Channel, enhanced Ethernet and high-performance computing (HPC) clustered traffic within the data center. FCoE support will require new HBAs and switches and will likely rely upon a 10 Gbps Ethernet infrastructure. The formal proposal for FCoE is already in the hands of an ANSI T11 committee. Experts and vendors suggest that FCoE standards and products should appear sometime in 2009. Users watching the development of FCoE will probably limit their SAN expansion plans until new FCoE HBAs and other components become available.
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