diff --git a/plugins/solaris/io_disk b/plugins/solaris/io_disk
index 8ea87e0d..509cf1ca 100755
--- a/plugins/solaris/io_disk
+++ b/plugins/solaris/io_disk
@@ -12,6 +12,7 @@
      busy    : similar to iostat %b, %w (%w usually indicates 0 in Sol10,11)
      queue   : similar to iostat actv, wait
      latency : similar to iostat asvc_t, wsvc_t
+     size    : average io size
 
   This plugin is improved from Solaris io_busy_, io_ops_, io_bytes_ plugins.
   Any device found in /usr/bin/kstat can be monitored.
@@ -52,7 +53,7 @@
     It may be good to link like ln -s /path/to/io_disk io_nfs if necessary.
 
   env.module_regex - kstat module. See man kstat -m option.
-    example:  env.module_regex  /^(s?sd|vdc|zvblk|dad|md|nfs|tape)$/
+    example:  env.module_regex  /^(s?sd|vdc|zvblk|dad|md|nfs|st)$/
     default:  /^(s?sd|vdc|zvblk|dad|md)$/
 
   env.title_type - Device type shown in graph title.
@@ -92,7 +93,7 @@ set -o nounset  # Like perl use strict;
 
 # Set environment variables
 plugin_name=io
-functions='ops bytes busy queue latency'
+functions='ops bytes busy queue latency size'
 : "${class:=disk}"
 : "${module:=sd}"
 : "${module_regex:=/^(s?sd|vdc|zvblk|dad|md)\$/}"
@@ -120,43 +121,57 @@ preconfig() {
     case "$func" in
     ops)
         conf_title='I/O Operations'
-        conf_in=reads
-        conf_out=writes
-        conf_cdef=
         conf_gargs='--base 1000'
         conf_vlabel='Ops per second write (-) / read (+)'
+        conf_in=reads
+        conf_out=writes
+        conf_in_cdef=
+        conf_out_cdef=
         ;;
     bytes)
         conf_title='I/O Throughput'
-        conf_in=nread
-        conf_out=nwritten
-        conf_cdef=
         conf_gargs='--base 1024'
         conf_vlabel='Bytes per second write (-) / read (+)'
+        conf_in=nread
+        conf_out=nwritten
+        conf_in_cdef=
+        conf_out_cdef=
         ;;
     busy)
         conf_title='Busy & Wait'
-        conf_in=rtime
-        conf_out=wtime
-        conf_cdef=',100,*'
         conf_gargs='--base 1000 --lower-limit 0 --upper-limit 100'
         conf_vlabel='% wait (-) / busy (+)'
+        conf_in=rtime
+        conf_out=wtime
+        conf_in_cdef=',100,*'
+        conf_out_cdef=',100,*'
         ;;
     queue)
         conf_title='Queue Length'
-        conf_in=rlentime
-        conf_out=wlentime
-        conf_cdef=
         conf_gargs='--base 1000'
         conf_vlabel='Queue length wait (-) / actv (+)'
+        conf_in=rlentime
+        conf_out=wlentime
+        conf_in_cdef=
+        conf_out_cdef=
         ;;
     latency)
         conf_title='Latency'
-        conf_in=rlentime
-        conf_out=wlentime
-        conf_cdef=
         conf_gargs='--base 1000'
         conf_vlabel='Seconds wsvc_t (-) / asvc_t (+)'
+        conf_in=rlentime
+        conf_out=wlentime
+        conf_in_cdef=
+        conf_out_cdef=
+        ;;
+    size)
+        conf_title='I/O Size'
+        conf_gargs='--base 1024'
+        conf_vlabel='Average size write (-) / read (+)'
+        conf_in=nread
+        conf_out=nwritten
+        conf_in_cdef=
+        conf_out_cdef=
         ;;
     *)
         echo "Unknown function: $func"
@@ -205,8 +220,9 @@ do_config() {
         ref="name_$dev"
         devname=${!ref:-}  # ${!varname} means indirect evaluation (similar to eval)
 
-        # reads and writes are necessary to calculate latency
-        if [ "$func" = 'latency' ]; then
+        # reads and writes are necessary to calculate latency, size
+        case "$func" in
+        latency|size)
             for stat in reads writes
             do
                 echo "${dev}_$stat.label dummy" 
@@ -214,23 +230,37 @@ do_config() {
                 echo "${dev}_$stat.type DERIVE"
                 echo "${dev}_$stat.min 0"
             done
-            # rlentime / ( reads + writes )
-            conf_cdef=,${dev}_reads,${dev}_writes,+,/
-        fi
+            ;;
+        esac
 
+        # Set cdef for latency, size
+        case "$func" in
+        latency)
+            # rlentime / ( reads + writes )
+            conf_in_cdef=,${dev}_reads,${dev}_writes,+,/
+            conf_out_cdef=,${dev}_reads,${dev}_writes,+,/
+            ;;
+        size)
+            conf_in_cdef=,${dev}_reads,/
+            conf_out_cdef=,${dev}_writes,/
+            ;;
+        esac
+
+        # Print data attributes
         echo "${dev}_${conf_out}.label dummy" 
         echo "${dev}_${conf_out}.graph no"
         echo "${dev}_${conf_out}.type DERIVE"
         echo "${dev}_${conf_out}.min 0"
+        if [ -n "${conf_out_cdef:-}" ]; then
+            echo "${dev}_${conf_out}.cdef ${dev}_${conf_out}${conf_out_cdef}"
+        fi
 
         echo "${dev}_${conf_in}.label ${devname:-${dev}}"
         echo "${dev}_${conf_in}.negative ${dev}_${conf_out}"
         echo "${dev}_${conf_in}.type DERIVE"
         echo "${dev}_${conf_in}.min 0"
-
-        if [ -n "$conf_cdef" ]; then
-            echo "${dev}_${conf_out}.cdef ${dev}_${conf_out}${conf_cdef}"
-            echo "${dev}_${conf_in}.cdef ${dev}_${conf_in}${conf_cdef}"
+        if [ -n "${conf_in_cdef:-}" ]; then
+            echo "${dev}_${conf_in}.cdef ${dev}_${conf_in}${conf_in_cdef}"
         fi
     done
 
@@ -243,11 +273,14 @@ do_getvalue() {
     func=$1
     preconfig "$func"
 
-    if [ "$func" = 'latency' ]; then
+    case "$func" in
+    latency|size)
         stat_regex="/^($conf_in|$conf_out|reads|writes)\$/"
-    else
+        ;;
+    *)
         stat_regex="/^($conf_in|$conf_out)\$/"
-    fi
+        ;;
+    esac
 
     echo "multigraph ${plugin_name}_${func}_${module}"