The best way to see if disk IO is the problem is to run iostat. I run
"iostat -x 10" as I find that if a disk is at high load for 10
seconds that
usually means that there is a serious performance issue. In the top
output
you can see that multiple users have IMAP processes blocked on disk
IO which
is an indication that disk IO speed is probably the issue.
The mail server VM
iostat -x 10
Linux 2.6.32-573.12.1.el6.x86_64 (clients.webgen.com.au) 19/01/16
_x86_64_ (5 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
1.56 0.01 0.58 4.68 0.04 93.14
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
avgrq-sz avgqu-sz await svctm %util
vda 1.20 14.03 1.51 4.86 60.27 145.11
32.21 0.21 33.21 6.05 3.86
vdb 0.08 19.10 10.89 0.84 982.21 161.89
97.52 0.27 22.99 6.96 8.17
vdc 0.30 8.25 18.70 11.90 1396.54 158.89
50.83 1.98 64.62 3.61 11.05
dm-0 0.00 0.00 1.35 17.22 49.29 137.51
10.06 0.19 10.34 1.72 3.20
dm-1 0.00 0.00 1.37 0.95 10.96 7.59
8.00 1.08 467.01 4.59 1.06
dm-2 0.00 0.00 19.03 20.11 1396.54 158.89
39.74 1.46 37.35 2.82 11.05
dm-3 0.00 0.00 10.97 20.24 982.21 161.89
36.66 0.98 31.25 2.62 8.17
avg-cpu: %user %nice %system %iowait %steal %idle
1.17 0.00 0.70 44.64 0.06 53.43
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
avgrq-sz avgqu-sz await svctm %util
vda 0.90 5.20 3.00 3.70 96.80 68.00
24.60 0.79 117.54 31.31 20.98
vdb 0.20 57.90 126.70 1.70 4590.40 475.20
39.45 2.77 21.47 7.72 99.17
vdc 0.00 3.20 68.90 15.80 1103.20 147.20
14.76 4.56 53.92 11.70 99.09
dm-0 0.00 0.00 1.70 8.40 78.40 67.20
14.42 1.59 157.81 19.95 20.15
dm-1 0.00 0.00 0.00 0.10 0.00 0.80
8.00 0.00 3.00 3.00 0.03
dm-2 0.00 0.00 68.70 18.80 1102.40 147.20
14.28 4.61 52.67 11.32 99.09
dm-3 0.00 0.00 126.80 59.40 4588.80 475.20
27.20 3.81 20.43 5.33 99.17
avg-cpu: %user %nice %system %iowait %steal %idle
0.92 0.00 0.56 41.01 0.04 57.46
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
avgrq-sz avgqu-sz await svctm %util
vda 0.00 7.00 0.00 2.60 0.00 72.00
27.69 0.14 55.31 43.92 11.42
vdb 0.00 2.20 101.20 1.10 5320.80 31.20
52.32 1.21 11.92 9.68 99.01
vdc 0.60 2.30 104.10 2.10 1779.20 33.60
17.07 1.33 12.49 9.39 99.75
dm-0 0.00 0.00 0.00 9.00 0.00 72.00
8.00 0.81 90.49 12.69 11.42
dm-1 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00
dm-2 0.00 0.00 104.70 4.20 1779.20 33.60
16.65 1.34 12.29 9.16 99.75
dm-3 0.00 0.00 101.20 3.90 5319.20 31.20
50.91 1.21 11.62 9.42 99.01
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