Monitoring Exadata Storage Cells - Oracle Exadata Recipes: A Problem-Solution Approach - page 396

How It Works
On Exadata Storage Servers, small I/O requests are defined as I/O requests smaller than 128 KB and large I/O requests
are larger than 128 KB. Each cell disk I/O metric has both a small I/O and large I/O measurement. This is important
on Exadata because large I/O requests are more likely to yield cell offload and Smart Scan performance savings.
Measuring the ratio of small I/O requests to large I/O requests, then, can be a mechanism to measure the likelihood of
your workload from being able to leverage some of Exadata's important performance features.
In the solution of this recipe, we used CellCLI's list metriccurrent command for the small I/O and large I/O
IOPs-related metrics for both hard disks and flash disks and reported on the total number of requests along with the
ratio between the two types.
13-10. Detecting Grid Disk I/O Bottlenecks
Problem
You wish to diagnose Exadata grid disk I/O bottlenecks on your Exadata storage grid.
Solution
In this recipe, you will learn how to use Exadata's GRIDDISK metrics to measure I/O bottlenecks for your Exadata grid
disks. Execute the script in Listing 13-7, which will display I/O statistics for your grid disks in which the metric values
exceed predefined thresholds.
Listing 13-7. lst13-07-griddisk-iostats.sh
#!/bin/sh
# Name: lst13-08-griddisk-iostats.sh
# Purpose: Show current grid disk metrics
# Usage: ./lst13-08-griddisk-iostats.sh [metriccurrent|metrichistory]
SCOPE=$1 # run with either metriccurrent or metrichistory
# Adjust the following to suit your needs
CELLGROUP=/home/oracle/cell_group
MBMIN=1 ## 1 MB/second per disk
IORQMIN=120 ## 10 IOPs per disk
LATMIN=10000 ## 10 ms latency
########################################
## Metrics list per type #####################################################
MBPS="GD_IO_BY_R_LG_SEC GD_IO_BY_R_SM_SEC GD_IO_BY_W_LG_SEC GD_IO_BY_W_SM_SEC"
IORQ="GD_IO_RQ_R_LG_SEC GD_IO_RQ_R_SM_SEC GD_IO_RQ_W_LG_SEC GD_IO_RQ_W_SM_SEC"
LAT="GD_IO_TM_R_LG_RQ GD_IO_TM_R_SM_RQ GD_IO_TM_W_LG_RQ GD_IO_TM_W_SM_RQ"
##############################################################################
# dcli/cellcli commands
for met in $MBPS
do
echo "Listing ${SCOPE} for ${met} when IO rate > ${MBMIN} MB/second"
dcli -g ${CELLGROUP} "cellcli -e list ${SCOPE} \