HP StorageWorks XP Disk Array Mainframe Host Attachment and Operations Guide XP24000, XP20000 (A5951 - 96151, September 2007)

For example, for ESCON, you can configure four or eight paths per path group from a host to a
storage unit.
For ESCON, you can configure at least four paths in the path group to maximize performance. Most
ESCON controllers initiate channel command execution that partially synchronizes the lower disk
drive interface with the upper channel interface. This channel command allows you only a very short
time to reconnect. The consequence of limited time is a reconnection that can fail. Having eight paths
in the path group minimizes the number of missed reconnections. Increasing the number of path
groups does not minimize the number of missed reconnections substantially. If you use eight paths in
path groups, you can increase the overall throughput.
For FICON controllers, there is no synchronization between the lower disk drive interface and the
upper channel interface. The number of paths in the path group depends on the throughput requirement.
If it takes x paths to satisfy the throughput requirement, where x is the number of paths, set the path
group to x.
NOTE:
x must be a minimum of two and cannot exceed a maximum of eight.
Attaching ESCON Channel Adapters
You can attach the XP disk array storage unit to a host system using ESCON adapters.
For zSeries host attachment using ESCON, only the first 16 addresses of the LSSs can be used. The
ranges of supported device addresses may be noncontiguous. Devices that are not mapped to a
logical device respond and show address exceptions.
When a primary controller connects to a secondary controller, the primary connection converts to a
channel. The controller images can handle ESCON interconnections as follows:
• 1-256 devices (bases and aliases) per controller image
• 1-4096 devices (bases and aliases) with 16 controller images
• 1-512 logical paths per controller image v 1 - 64 logical paths per ESCON port (shared by all
controller images)
• 256 path groups per control unit ImageHost adapters, cables, distances, and specifications for
ESCON adapters on zSeries hosts
Using ESCON adapters, the storage unit provides the following configurations:
• A maximum of 64 host ports
• A maximum of 64 logical paths per port to 16 control-unit images (4096 CKD devices) over a
single ESCON port on the storage unit
• Zero to 64 ESCON channels, two per ESCON host adapter
• Two ESCON links with each link that supports up to 64 logical paths
• Up to 16 host adapters that provide a maximum of 32 ESCON links per machine
• Up to 32 host adapters providing a maximum of 64 ESCON links per machine
FICON and ESCON Host Attachment22