FICON Express2 Channel Performance Version 1.0 - IBM

FICON Express2 Channel Performance Version 1.0
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The first column “PORT ADDR” identifies the switch port address. The 2nd and 3rd
“CONNECTION” columns identify what this switch port is connected to. The “UNIT”
indicates whether is it a channel (CHP-H), a control unit port (CU) or in the case where two
directors are cascaded, another switch port (SWITCH). The “ID” in column 3 is the CHPID
number for the channel or the control unit address for the CU. The values in the “AVG
FRAME PACING” column will be zero most of the time. This column is intended to display
the amount of time that a frame is delayed when there are no more buffer credits available.
The “AVG FRAME SIZE” columns display the average number of bytes per frame being
“READ” into that director port or written out from that director port. These columns can be
used to help understand if your workload is a processor or bus/link limited workload. The
maximum frame size is 2K bytes. If your workload is transferring a small amount of data
using small block sizes, such as the 4K bytes per I/O typically found in online transaction
processing, then the average frame size will most likely be less than 1000 bytes and your
workload will most likely be channel processor or control unit port processor limited. On the
other hand, if your workload transfers a lot of data using large block sizes, then the average
frame size will most likely be in the 1500 to 2000 byte range and your workload will most
likely be channel or control unit bus or link limited. Figure 25 is an example of a workload
that is in between these two extremes and has an average frame size of 1334 bytes. In this
case, both processor and bus/link utilizations should be monitored.
The last two columns on this report, the “PORT BANDWIDTH (MB/SEC)” “READ” and
“WRITE” columns contain the MB/sec that are being “READ” into that director port or
written out from that director port. Please note that for an RMF interval where 10 MB/sec of
data is being “READ” from a device on a control unit that the 10 MB/sec value will appear
on the line for the director port connected to the control unit in the “READ” column but in
the “WRITE” column for the director port connected to the channel in the RMF FICON
Director Activity Report and in the “READ(MB/SEC)” column of the channel in the RMF
Channel Activity Report. The “READs” and “WRITEs” on the FICON Director Activity
report are from the perspective of the port, whereas the “READs” and “WRITEs” on the
Channel Activity report are from the perspective of the higher level application. Figure 25 is
an example of a benchmark measurement where about 40 MB/sec was “READ” from each of
3 different control unit ports and over 120 MB/sec was written to a single channel, CHPID
#95.
To convert control unit port MB/sec data into control unit port utilizations, you also need to
know what the maximum capability of the control unit port is for both small and large block
sizes and whether your workload is a small or large block size workload. If a control unit
vendor tells you or you run your own test to determine that the maximum capability of a
single port on their box for 4k byte READs is 5000 I/Os per second, then this is the same as