Brocade FICON Administrator's Guide v7.1.0 (53-1002753-01, March 2013)

FICON Administrator’s Guide 49
53-1002753-01
FICON emulation overview
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FIGURE 11 IBM z/OS Global Mirror emulation
Figure 11 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 the 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 or an FX8-24
blade with FICON emulation.
For information on configuring IBM z/OS Global Mirror emulation or XRC emulation, refer to
“Configuring FICON emulation” on page 54. For information on displaying IBM z/OS Global Mirror
emulation status and statistics, refer to “Displaying FICON emulation performance statistics” on
page 55.
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 non-conforming 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.
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Brocade
FICON
Directors
Brocade
extension switch
with emulation
for FICON
Brocade
extension switch
with emulation
for FICON
Brocade
FICON
Directors
System z
hosts
IBM Z/OS global
mirror system
data mover
Primary disk
volumes
Secondary disk
volumes
IP network
IP network