LP #952727: pt-diskstats shows incorrect wr_mb_s

**Reported in Launchpad by Vadim Tkachenko last update 19-06-2012 20:02:23

iostat -dxm 5 shows:
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
fioa 0.00 0.00 0.00 7765.00 0.00 121.32 32.00 0.00 4.02 0.00 0.00
fiob 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 0.20 0.00 0.60 0.00 0.00 10.67 0.00 0.00 0.00 0.00
sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
fioa 0.00 0.00 0.00 7540.40 0.00 117.82 32.00 0.00 4.00 0.00 0.00
fiob 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
fioa 0.00 0.00 0.00 7500.20 0.00 117.18 32.00 0.00 3.98 0.00 0.00
fiob 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 0.20 0.00 0.60 0.00 0.00 10.67 0.00 0.00 0.00 0.00
sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
fioa 0.00 0.00 0.00 7452.80 0.00 116.44 32.00 20.08 4.03 0.02 15.94
fiob 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
sda 6.20 0.00 0.80 0.20 0.03 0.00 57.60 0.03 31.80 22.00 2.20
sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
fioa 0.00 0.00 0.00 7450.40 0.00 116.41 32.00 20.22 4.02 0.02 15.92
fiob 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

pt-diskstat shows
#ts device rd_s rd_avkb rd_mb_s rd_mrg rd_cnc rd_rt wr_s wr_avkb wr_mb_s wr_mrg wr_cnc wr_rt busy in_prg io_s qtime stime

{160}

fioa 0.1 4.0 0.0 0% 0.0 26.6 30924.6 6.0 181.5 0% 777.5 25.1 47% 0 30924.6 23.3 0.0

{161}

fioa 0.1 4.0 0.0 0% 0.0 26.6 30778.5 6.0 181.1 0% 772.9 25.1 47% 0 30778.6 23.2 0.0

{162}

fioa 0.1 4.0 0.0 0% 0.0 26.6 30634.3 6.0 180.7 0% 768.3 25.1 46% 0 30634.4 23.2 0.0

{163}

fioa 0.1 4.0 0.0 0% 0.0 26.6 30492.0 6.1 180.3 0% 763.7 25.0 46% 0 30492.1 23.1 0.0

{164}

fioa 0.1 4.0 0.0 0% 0.0 26.6 30352.7 6.1 179.9 0% 759.2 25.0 46% 0 30352.8 23.1 0.0

while sysbench is:
[ 280s] reads: 0.00 MB/s writes: 120.01 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)
[ 290s] reads: 0.00 MB/s writes: 116.24 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)
[ 300s] reads: 0.00 MB/s writes: 121.96 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)
[ 310s] reads: 0.00 MB/s writes: 118.33 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)
[ 320s] reads: 0.00 MB/s writes: 114.20 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)
[ 330s] reads: 0.00 MB/s writes: 118.77 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)
[ 340s] reads: 0.00 MB/s writes: 119.28 MB/s fsyncs: 0.00/s response time: 0.045ms (95%)

so device is doing close to 120 MB/s,
while
pt-diskstats shows 180

I am using async io mode in sysbench