Sar: why is %util for a multipathed device not the same as %util added up for all its paths?
Issue
-
With multipath device and 8 paths, why doesn't the %util from each path added up correspond to the %util from the multipathed device?
- For example from the following sar output, there are 4 active paths to the storage (dev8-16, dev8-48, dev8-80 and dev8-112) having 35.50, 34.19, 32.26 and 33.72 as their respective values for %util. Combining them would bring you a total of 135.67. The multipathed device dev253-12 (which is backed by the 8 paths) only has 97.48 % utilization. How can this be explained?
00:00:01 DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util 12:35:01 dev8-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 12:35:01 dev8-16 719.94 71100.04 0.11 98.76 0.66 0.92 0.49 35.50 12:35:01 dev8-32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 12:35:01 dev8-48 717.35 71100.92 0.13 99.12 0.59 0.82 0.48 34.19 12:35:01 dev8-64 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 12:35:01 dev8-80 698.86 71102.33 0.21 101.74 0.59 0.85 0.46 32.26 12:35:01 dev8-96 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 12:35:01 dev8-112 662.44 71099.91 0.27 107.33 0.58 0.88 0.51 33.72 12:35:01 dev253-12 35550.38 284402.35 0.72 8.00 46.35 1.30 0.03 97.48
Subscriber exclusive content
A Red Hat subscription provides unlimited access to our knowledgebase of over 48,000 articles and solutions.
Welcome! Check out the Getting Started with Red Hat page for quick tours and guides for common tasks.
