HP StorageWorks SN6000 Fibre Channel Switch Installation and Reference Guide 23
Latency
Latency is a measure of how fast a frame travels through a switch from one port to another. The factors that
affect latency include transmission rate and the source/destination port relationship (Table 5).
Feature licenses
A license key provides a way to expand the capabilities of your switch and fabric as your needs grow. The
HP StorageWorks SN6000 Stackable 20Gb ISL Upgrade LTU enables the XPAK ports to transmit at 20
Gb/s instead of the default 10 Gb/s. Applying a license key is not disruptive, nor does it require a switch
reset. To order a license key, contact your switch distributor or your authorized reseller. For more
information, see ”Installing feature license keys” on page 46.
Multiple switch fabrics
By connecting switches to one another, you can expand the number of available ports for devices. Each
switch in the fabric is identified by a unique domain ID, and the fabric can automatically resolve domain ID
conflicts. Because the Fibre Channel ports are self-configuring, you can connect SN6000 Fibre Channel
Switches together in a wide variety of topologies. When planning your fabric, consider your topology and
cabling requirements. Transparent routing to a legacy fabric is also possible using TR_Ports.
For more information about Storage Area Network (SAN) connectivity, see the SAN Design Reference
Guide available at the HP website: http://www.hp.com/go/SANdesignguide
.
The following topics describe important aspects of multiple switch fabrics:
• Optimizing device performance, page 23
• Domain ID, principal priority, and domain ID lock, page 24
• Common topologies, page 26
• Transparent routing, page 26
Optimizing device performance
When choosing a topology for a multiple switch fabric, you should also consider the proximity of your
server and storage devices and the performance requirements of your application. Storage applications
such as video distribution, medical record storage/retrieval, or real-time data acquisition can have specific
latency or bandwidth requirements.
The SN6000 Fibre Channel Switch provides the lowest latency of any product in its class. For information
about latency, see ”Performance” on page 22. However, the highest performance is achieved on Fibre
Channel switches by keeping traffic within a single switch instead of relying on ISLs. Therefore, for optimal
device performance, place devices on the same switch under the following conditions:
• Heavy I/O traffic between specific server and storage devices.
• Distinct speed mismatch between devices such as the following:
• An 8 Gb/s server and a slower 4 Gb/s storage device
• A high performance server and a slow tape storage device
Table 5 Port-to-port latency
Destination Rate
Source
Rate
Gb/s2481020
2 < 0.6 sec < 0.7 sec
1
< 0.6 sec
1
< 0.6 sec1 < 0.6 sec1
4 < 0.4 sec < 0.3 sec < 0.4 sec
1
< 0.4 sec1 < 0.3 sec1
8 < 0.3 sec < 0.2 sec < 0.2 sec < 0.2 sec1 < 0.2 sec1
10 < 0.3 sec < 0.3 sec < 0.2 sec < 0.2 sec < 0.2 sec1
20 < 0.3 sec < 0.2 sec < 0.2 sec < 0.2 sec < 0.2 sec
1 Based on minimum frame size of 36 bytes. Latency increases for larger frame sizes.
