Texas Memory Systems RamSan-500 - Manual (Page 9)

RamSan-500 User’s Manual 9 of 48
connections requires one of the following solutions: multi-pathing
software to a single LUN, using software to stripe across multiple LUNs,
accessing multiple LUNs on the RamSan-500 concurrently, or
connecting multiple servers to the system.
3.1.2 3.1.2 3.1.2 3.1.2 Host Bus Adapter Host Bus Adapter Host Bus Adapter Host Bus Adapter
You can modify some HBA settings to increase performance. For
information specific to your HBA, consult the HBA documentation. Note
that many settings are intended to increase the performance of slow
storage devices and will not be applicable to RamSans. 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.
3.1.3 3.1.3 3.1.3 3.1.3 PCI PCI PCI PCI B B B Bus us us us
High bandwidth HBA traffic can quickly inundate slower PCI buses.
Once a PCI bus reaches its limit, you can do very little to improve
performance. Many servers, however, provide different PCI buses with
different speeds, and placing the HBA on a different PCI bus can
improve performance. TMS recommends giving each 4-gigabit 2 port
HBA at least an entire PCIX bus or a PCI Express (PCIe) slot.
3.1.4 3.1.4 3.1.4 3.1.4 C C C CPU PU PU PU
At a certain point, CPU performance can limit data transfer rates.
Determine whether the server’s CPU resources are the limiting factor
in performance while benchmarking the RamSan-500 as a raw physical
device. Otherwise, an improperly tuned file system or application can
make the CPU appear to be the limiting factor when it is not. Perform
raw device testing after setting up any multi-pathing.
There are a few ways to decrease CPU usage without increasing CPU
resources. Certain data usage patterns can be very CPU intensive and
fully utilize the CPU. These usually involve small transfer sizes. When
possible, increasing the average transfer size decreases CPU usage
and offers better performance. Another way to decrease CPU usage is
by enabling interrupt coalescing. Interrupt coalescing is an HBA
dependent feature that offers a method to trade latency for CPU usage.
This feature delays calling the HBA transfer interrupt until several
transfers are ready. In general, TMS does not recommend enabling
Interrupt Coalescing, because most RamSan applications benefit from
low latency. For more information, consult your HBA documentation.
3.2 Connecting the Fibre Channel Ports
Connect the Fibre Channel ports on the RamSan-500 to your server or to
a Fibre Channel switch.