FW V06.XX/HAFM SW V08.02.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DD-TE, July 2004)
Table Of Contents
- SAN HA Planning Guide
- Contents
- About this Guide
- Introduction to HP Fibre Channel Products
- Product Management
- Planning Considerations for Fibre Channel Topologies
- Fibre Channel Topologies
- Planning for Point-to-Point Connectivity
- Characteristics of Arbitrated Loop Operation
- Planning for Private Arbitrated Loop Connectivity
- Planning for Fabric-Attached Loop Connectivity
- Planning for Multi-Switch Fabric Support
- Fabric Topologies
- Planning a Fibre Channel Fabric Topology
- Fabric Topology Design Considerations
- FICON Cascading
- Physical Planning Considerations
- Port Connectivity and Fiber-Optic Cabling
- HAFM Appliance, LAN, and Remote Access Support
- Inband Management Access (Optional)
- Security Provisions
- Optional Features
- Configuration Planning Tasks
- Task 1: Prepare a Site Plan
- Task 2: Plan Fibre Channel Cable Routing
- Task 3: Consider Interoperability with Fabric Elements and End Devices
- Task 4: Plan Console Management Support
- Task 5: Plan Ethernet Access
- Task 6: Plan Network Addresses
- Task 7: Plan SNMP Support (Optional)
- Task 8: Plan E-Mail Notification (Optional)
- Task 9: Establish Product and HAFM Appliance Security Measures
- Task 10: Plan Phone Connections
- Task 11: Diagram the Planned Configuration
- Task 12: Assign Port Names and Nicknames
- Task 13: Complete the Planning Worksheet
- Task 14: Plan AC Power
- Task 15: Plan a Multi-Switch Fabric (Optional)
- Task 16: Plan Zone Sets for Multiple Products (Optional)
- Index
Planning Considerations for Fibre Channel Topologies
101SAN High Availability Planning Guide
ISL Oversubscription
ISL oversubscription (or congestion) occurs when multiplexed traffic from
several devices is transmitted across a single ISL. When an ISL is oversubscribed,
fabric elements use fairness algorithms to interleave data frames from multiple
devices, thus giving fractional bandwidth to the affected devices. Although all
devices are serviced, ISL and fabric performance is reduced.
Figure 41 illustrates ISL oversubscription. Two NT servers, each with maximum
I/O of 100 MBps, are contending for the bandwidth of a single ISL operating at
1.0625 Gbps. In addition to data, the ISL must also transmit Class F traffic
internal to the fabric. When operating at peak load, each NT server receives less
than half the available ISL bandwidth.
Figure 41: ISL oversubscription
Depending on fabric performance requirements and cost, there are several options
to solve ISL oversubscription problems, including:
■ Employ device locality — NT server 1 and its associated storage device can
be connected through one director. NT server 2 and its associated storage
device can be connected through the other director. As a result, minimal
traffic flows across the ISL between directors and the congestion problem is
mitigated. For additional information, refer to “Device Locality” on page 102.
NT Server 1
(100 MBps Max)
1 Gbps ISL
Storage
NT Server 2
(100 MBps Max)
T
M
T
M
1
5
10 15
20
25
0
100
150
200
Time (Sec)
Bandwidth (MBps)
50
1 Gbps ISL
NT Server 1
NT Server 2