Texas Memory Systems RamSan-500 - Manual (Page 8)

RamSan-500 User’s Manual 8 of 48
Chapter 3 – Connections
3.1 Installing a Host Bus Adaptor in the Host System
Host Bus Adapters (HBAs) provide an interface from the server’s PCI bus
to Fibre Channel attached devices. HBAs are available from a variety of
vendors. Before purchasing an HBA, ensure that it provides a driver for
the Operating System (OS) version that you are using.
Before installing the HBA, consult your server’s documentation to
determine which one of its PCI slots is on the fastest and least congested
PCI bus (see Section 3.1.3, below, for details). Next, power down your
server and place the HBA in this slot. Power on your server and follow the
instructions provided with the HBA to install the driver. It is generally a
good idea to check the HBA provider’s Web site to obtain the latest drivers
and firmware for the HBA. Updated drivers may include new features,
improved performance, and minor bug fixes.
T ROUBLESHOOTING T IP :
I F YOU ENCOUNTER ANY PROBLEMS WITH THE HBA, THE FIRST STEP IN THE DEBUGGING
PROCESS IS VERIFYING THAT YOU ARE USING THE LATEST DRIVER AND FIRMWARE .
The speed of the server and network interface ultimately limit the
RamSan-500’s capabilities. A few different components can affect the
maximum performance of the RamSan-500, including FC interfaces, Host
Bus Adapters, PCI buses, and server CPU resources.
3.1.1 3.1.1 3.1.1 3.1.1 Fibre Channel Fibre Channel Fibre Channel Fibre Channel IIIInterface nterface nterface nterface
Currently, the RamSan supports two Fibre Channel communication
speeds: 2- and 4-gigabit. Accounting for encoding and overhead, these
transfer rates allow data to be transmitted to the RamSan-500 at a
half duplex rate of ~200 MB/s and ~400 MB/s, for 2- and 4-gigabit,
respectively. 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 (due to the individual
half duplex limits). To find the maximum for other data usage patterns,
use the following formula (4-gigabit HBA):
( Smaller usage percentage / Larger ) x 400MB/s + 400MB/s
For example, to calculate a data usage pattern with 66% reads and
33% writes:
( 33 / 66 ) x 400 + 400 = 600 MB/s
Many applications require storage bandwidth that exceeds what a
single FC connection can provide. To accommodate this situation, we
provide up to 8 FC ports per RamSan-500, each of which can supply
the bandwidth described above. Using multiple Fibre Channel