Tape emulation – Brocade FICON Administrator’s Guide (Supporting Fabric OS v7.3.0) User Manual
Page 69
primary volume to be located at a distance from its mirrored secondary without encountering
performance degradation associated with IU pacing.
FIGURE 17 IBM z/OS Global Mirror emulation
The figure above shows how the primary volume and the secondary mirrored volume may be
geographically distant across an IP WAN. Updates to the primary disk volumes are completed by the
production applications and then staged in a control unit cache to be read by SDM. SDM then writes the
updates to the secondary volumes. The latency introduced by greater distance creates delays in
anticipated responses to certain commands. The FICON IU pacing mechanism may interpret delays as
an indication of a large data transfer that could monopolize a shared resource and react by throttling the
I/O. IBM z/OS Global Mirror emulation provides local responses to remote hosts, eliminating distance-
related delays. You can use the Brocade 7800 switch, Brocade 7840 switch, or an FX8-24 blade with
FICON emulation.
For information on configuring IBM z/OS Global Mirror emulation, refer to
on page 72. For information on displaying IBM z/OS Global Mirror emulation status and statistics,
refer to
Displaying FICON emulation performance statistics
on page 73.
Tape emulation
Tape emulation (also called tape pipelining) refers to the concept of maintaining a series of I/O
operations across a host-WAN-device environment and should not be confused with the normal FICON
streaming of CCWs and data in a single command chain. Normally, tape access methods can be
expected to read data sequentially until they reach the end-of-file delimiters (tape marks) or to write
data sequentially until either the data set is closed or an end-of-tape condition occurs (multi-volume file).
The emulation design strategy attempts to optimize performance for sequential reads and writes, while
accommodating any other nonconforming conditions in a lower performance non-emulating frame
shuttle. Because write operations can be expected to comprise the larger percentage of I/O operations
for tape devices (for archival purposes), they are addressed first.
For information on configuring tape emulation, refer to
on page 72. For
information on displaying tape emulation status and statistics, refer to
on page 73.
Tape emulation
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