Hi,
I have a mirrored logical volume with a in memory log (core log), built on top of 2 multipath'ed devices, for which I'm getting
weird perf data collected by sysstat (sar -d).
To summarize, the transfers/s metric (tps) for the devmapper managed devices (mpath/lv_mimage,lv) show values up to 7 times greater
than the values I get per physical path.
I don't think the devicemapper overhead (if any) explains this (8 times), but I can't figure out how to interpret this.
* Logical volume lvol1 is the only lv on VG vg10 and is mirrored (corelog) on top of /dev/mapper/mpath10 and /dev/mapper/mpath1.
* Each mpath device is made of 4 physical paths, in a multibus setup (round robin)
* PE size on VG10 is 4MB
* /dev/mapper/vg10-lvol1 is has a ext3 fs with a block size of 4kB, journal size is 128 MB
* perfdata is collected with a sar -d 1 7200 -f mysarfile
Below an example of what I'm getting
Each mirror leg, vg10-lvol1_mimage_0 corresponding to mpath10 and vg10-lvol1_mimage_1 corresponding to mpath1, show a transfer
rate of 25217 tps and while each underlying physical path show 800 ~ 1000 tps.
I expected to get ~ 4000 tps.
Raw results:
mpath10
Time DEV tps
08:07:33 PM dev253-7 25217.64
vg10-lvol1_mimage_0
Time DEV tps
08:07:33 PM dev253-112 25217.64
paths
Time DEV tps
08:07:33 PM dev8-0 1011.22
08:07:33 PM dev66-64 1074.55
08:07:33 PM dev68-128 1056.51
08:07:33 PM dev70-192 972.55
mpath10 (360060xxx) dm-7 HP,OPEN-V
[size=31G][features=0][hwhandler=0][rw]
\_ round-robin 0 [prio=0][active]
\_ 0:0:2:1 sdak 66:64 [active][undef]
\_ 0:0:0:1 sda 8:0 [active][undef]
\_ 2:0:0:1 sdbu 68:128 [active][undef]
\_ 2:0:2:1 sdde 70:192 [active][undef]
vg10-lvol1_mimage_1
Time DEV tps
08:07:33 PM dev253-111 25219.24
mpath1
Time DEV tps
08:07:33 PM dev253-16 25219.24
paths
Time DEV tps
08:07:33 PM dev65-32 810.82
08:07:33 PM dev67-96 757.11
08:07:33 PM dev69-160 818.64
08:07:33 PM dev71-224 787.58
mpath1 (360060yyy) dm-16 HP,OPEN-V
[size=31G][features=0][hwhandler=0][rw]
\_ round-robin 0 [prio=0][active]
\_ 0:0:3:1 sdbc 67:96 [active][undef]
\_ 2:0:1:1 sdcm 69:160 [active][undef]
\_ 2:0:3:1 sddw 71:224 [active][undef]
\_ 0:0:1:1 sds 65:32 [active][undef]
vg10-lvol1
Time DEV tps
08:07:33 PM dev253-113 18597.60
dumpe2fs -h /dev/mapper/vg10-lvol1
Block size: 4096
Fragment size: 4096
Fragments per group: 32768
Inode size: 128
Journal size: 128M
vgdisplay -v vg10
PE Size 4.00 MB
Rgds
Brem
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