IBM REDP-4285-00 User Manual
4285ch03.fm
Draft Document for Review May 4, 2007 11:35 am
86
Linux Performance and Tuning Guidelines
Example 3-2 vmstat output
[root@x232 root]# vmstat 2
r b swpd free buff cache si so bi bo in cs us sy id wa
2 1 0 9004 47196 1141672 0 0 0 950 149 74 87 13 0 0
0 2 0 9672 47224 1140924 0 0 12 42392 189 65 88 10 0 1
0 2 0 9276 47224 1141308 0 0 448 0 144 28 0 0 0 100
0 2 0 9160 47224 1141424 0 0 448 1764 149 66 0 1 0 99
0 2 0 9272 47224 1141280 0 0 448 60 155 46 0 1 0 99
0 2 0 9180 47228 1141360 0 0 6208 10730 425 413 0 3 0 97
1 0 0 9200 47228 1141340 0 0 11200 6 631 737 0 6 0 94
1 0 0 9756 47228 1140784 0 0 12224 3632 684 763 0 11 0 89
0 2 0 9448 47228 1141092 0 0 5824 25328 403 373 0 3 0 97
0 2 0 9740 47228 1140832 0 0 640 0 159 31 0 0 0 100
r b swpd free buff cache si so bi bo in cs us sy id wa
2 1 0 9004 47196 1141672 0 0 0 950 149 74 87 13 0 0
0 2 0 9672 47224 1140924 0 0 12 42392 189 65 88 10 0 1
0 2 0 9276 47224 1141308 0 0 448 0 144 28 0 0 0 100
0 2 0 9160 47224 1141424 0 0 448 1764 149 66 0 1 0 99
0 2 0 9272 47224 1141280 0 0 448 60 155 46 0 1 0 99
0 2 0 9180 47228 1141360 0 0 6208 10730 425 413 0 3 0 97
1 0 0 9200 47228 1141340 0 0 11200 6 631 737 0 6 0 94
1 0 0 9756 47228 1140784 0 0 12224 3632 684 763 0 11 0 89
0 2 0 9448 47228 1141092 0 0 5824 25328 403 373 0 3 0 97
0 2 0 9740 47228 1140832 0 0 640 0 159 31 0 0 0 100
iostat command
Performance problems can be encountered when too many files are opened, being read and
written to, then closed repeatedly. This could become apparent as seek times (the time it
takes to move to the exact track where the data is stored) start to increase. Using the iostat
tool, you can monitor the I/O device loading in real time. Different options enable you to drill
down even farther to gather the necessary data.
written to, then closed repeatedly. This could become apparent as seek times (the time it
takes to move to the exact track where the data is stored) start to increase. Using the iostat
tool, you can monitor the I/O device loading in real time. Different options enable you to drill
down even farther to gather the necessary data.
Example 3-3 shows a potential I/O bottleneck on the device /dev/sdb1. This output shows
average wait times (await) of about 2.7 seconds and service times (svctm) of 270 ms.
average wait times (await) of about 2.7 seconds and service times (svctm) of 270 ms.
Example 3-3 Sample of an I/O bottleneck as shown with iostat 2 -x /dev/sdb1
[root@x232 root]# iostat 2 -x /dev/sdb1
avg-cpu: %user %nice %sys %idle
11.50 0.00 2.00 86.50
11.50 0.00 2.00 86.50
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz
avgqu-sz await svctm %util
/dev/sdb1 441.00 3030.00 7.00 30.50 3584.00 24480.00 1792.00 12240.00 748.37
101.70 2717.33 266.67 100.00
avgqu-sz await svctm %util
/dev/sdb1 441.00 3030.00 7.00 30.50 3584.00 24480.00 1792.00 12240.00 748.37
101.70 2717.33 266.67 100.00
avg-cpu: %user %nice %sys %idle
10.50 0.00 1.00 88.50
10.50 0.00 1.00 88.50
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz
avgqu-sz await svctm %util
/dev/sdb1 441.00 3030.00 7.00 30.00 3584.00 24480.00 1792.00 12240.00 758.49
101.65 2739.19 270.27 100.00
avgqu-sz await svctm %util
/dev/sdb1 441.00 3030.00 7.00 30.00 3584.00 24480.00 1792.00 12240.00 758.49
101.65 2739.19 270.27 100.00
avg-cpu: %user %nice %sys %idle
10.95 0.00 1.00 88.06
10.95 0.00 1.00 88.06
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz
avgqu-sz await svctm %util
/dev/sdb1 438.81 3165.67 6.97 30.35 3566.17 25576.12 1783.08 12788.06 781.01
101.69 2728.00 268.00 100.00
avgqu-sz await svctm %util
/dev/sdb1 438.81 3165.67 6.97 30.35 3566.17 25576.12 1783.08 12788.06 781.01
101.69 2728.00 268.00 100.00
For a more detailed explanation of the fields, see the man page for iostat(1).