Fibre Channel Interface Bandwidth - IBM FlashSystem 710 User Manual

Ensure that the adapter that you select for use with the storage system provides a driver for the
operating system version that you are using.
Note: In subsequent sections, the term HBA is used to represent HCA or HBA interchangeably.
Before you install the HBA, consult your server documentation to determine which one of its PCI slots is
on the fastest and least congested PCI bus. Follow the instructions that are provided with the HBA to
install the card and driver. Obtain the latest drivers and firmware for the HBA. Updated drivers might
include new functions, improved performance, and minor bug fixes.
The speed of the server and network interface ultimately determine the storage system's capabilities.
Some components that can affect the maximum performance of the storage system include FC or
InfiniBand interfaces, host bus adapters, PCI buses, and server processor resources.

Fibre Channel interface bandwidth

Your storage system supports Fibre Channel (FC) communication speeds of 2 Gbps, 4 Gbps, or 8 Gbps.
Accounting for encoding and overhead, the maximum 8 Gbps transfer rate allows data to be transmitted
to the system at a half duplex rate of approximately 800 MBps. Fibre Channel interfaces have separate
read and write connections that allow a maximum data rate of twice the half-duplex rate. To sustain the
maximum full duplex rate, the data usage pattern of the system must be 50% read and 50% write. This
requirement is because of the individual half duplex limits. To find the maximum for other data usage
patterns, use the following formula (given an 8 Gb HBA):
[(smaller usage percentage/larger percentage) × 800 MBps] + 800 MBps
For example, to calculate a data usage pattern with 66% reads and 33% writes,
[(33/66) × 800] + 800 = 1200 MBps
Many applications require storage bandwidth that exceeds what a single FC connection can provide. To
accommodate this situation, up to 4 FC ports are available per system, each of which can supply the
bandwidth described here. Using multiple FC connections requires one of the following solutions:
multipathing software to a single logical unit, using software to stripe across multiple logical units,
accessing multiple logical units concurrently, or connecting multiple servers to the storage system.
Host bus adapter settings
You can modify some host bus adapter (HBA) settings to increase performance.
For information specific to your HBA, consult the HBA documentation. Many settings are intended to
increase the performance of slow storage devices and are not applicable to this high performance system.
In particular, it is always advisable to check the frame size. The amount of overhead for each Fibre
Channel frame is fixed, so larger frames have lower overhead. Set the frame size to the maximum setting,
generally 2048 bytes. For InfiniBand devices, also set the frame size to the maximum setting, generally
4096 bytes.
PCI bus selection and performance
High-bandwidth host bus adapter (HBA) traffic can quickly inundate slower PCI buses. When a PCI bus
reaches its limit, you can do little to improve performance.
Many servers, however, provide different PCI buses with different speeds, and placing the HBA on a
faster PCI bus can improve performance. When you install an 8 Gb, 2-port HBA in the server, allocate at
least an entire PCI-X bus or a PCI Express (PCIe) slot.
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IBM FlashSystem 710: User's Guide