Latency; Feature Licenses; Multiple Switch Fabrics; Optimizing Device Performance - HP AK241A - StorageWorks 8Gb Simple SAN Connection Installation And Reference Manual

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

Port-to-port latency

Destination Rate
Gbps
Source
2
Rate
4
8
1 Based on minimum frame size of 36 bytes. Latency increases for larger frame sizes.

Feature licenses

License keys provide a way to expand the capabilities of your switch and fabric as your needs grow. The
HP StorageWorks 8/20q 4-port Upgrade License activates additional Fibre Channel ports to 12, 16, or 20
ports. 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
license keys" on page 42.

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 8/20q 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
• Domain ID, principal priority, and domain ID
• Common topologies, page 22
• Transparent

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 8/20q Fibre Channel Switch provides the lowest latency of any product in its class. For information
about latency, see "Performance" on page 20. 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 slow tape storage device
2
< 0.6 μsec
< 0.4 μsec
< 0.3 μsec
performance, page 21
routing, page 23
4 8
1
< 0.7 μsec < 0.6 μsec
< 0.3 μsec < 0.4 μsec
< 0.2 μsec < 0.2 μsec
lock, page 22
8/20q Fibre Channel Switch Installation and Reference Guide
(Table 5).
1
1
"Installing feature
21