DMP is not slower than PowerPath. When we test with vxbench, the total time to complete each test is nearly the same. However, nmon shows the total system throughput as double with PowerPath which is incorrect because nmon is actually showing the throughput as double the true amount.. iostat -d, which shows IO stats for each disk, will show stats for hdisk devices and hdiskpower devices both and is actually showing the same IO in two places. So the PowerPath devices must be considered as additional disks by the OS since they are shown by iostat. We believe that nmon is counting the IO on the hdiskpower devices and on the hdisk devices so it shows the throughput as double the true value.

suggest to test performance via dd read/write (sequetial I/O) ,below is result , we can see DMP is a little better than PowerPath

PowerPath:
# time dd if=/dev/zero of=/dev/rhdiskpower0  bs=1024k count=5000
5000+0 records in.
5000+0 records out.

real    1m14.10s
user    0m0.01s
sys     0m1.48s

# time dd if=/dev/zero of=/dev/rhdiskpower0  bs=1024k count=5000
5000+0 records in.
5000+0 records out.

real    1m29.48s
user    0m0.01s
sys     0m1.49s

# time dd if=/dev/rhdiskpower0 of=/dev/null  bs=1024k count=5000
5000+0 records in.
5000+0 records out.

real    0m59.00s
user    0m0.01s
sys     0m0.62s

# time dd if=/dev/rhdiskpower0 of=/dev/null  bs=1024k count=5000
5000+0 records in.
5000+0 records out.

real    1m12.41s
user    0m0.01s
sys     0m0.63s


DMP:
# time dd if=/dev/zero of=/dev/vx/rdmp/emc0_32f9 bs=1m count=5000
5000+0 records in.
5000+0 records out.

real    0m56.17s
user    0m0.02s
sys     0m1.60s
# time dd if=/dev/zero of=/dev/vx/rdmp/emc0_32f9 bs=1m count=5000
5000+0 records in.
5000+0 records out.

real    0m55.93s
user    0m0.02s
sys     0m1.57s
# time dd if=/dev/zero of=/dev/vx/rdmp/emc0_32f9 bs=1m count=5000
5000+0 records in.
5000+0 records out.

real    1m28.67s
user    0m0.01s
sys     0m1.58s

# time dd if=/dev/vx/rdmp/emc0_32f9 of=/dev/null bs=1m count=5000
5000+0 records in.
5000+0 records out.

real    0m58.50s
user    0m0.02s
sys     0m0.71s
# time dd if=/dev/vx/rdmp/emc0_32f9 of=/dev/null bs=1m count=5000
5000+0 records in.
5000+0 records out.

real    1m14.63s
user    0m0.02s
sys     0m0.70s
#
 

Applies To

AIX 6.1
SF 5.1SP1RP2
EMC DMX3 storage

performance comparing between DMP and EMC PowerPath on AIX platform customer simulate heavy load on DMP device ( /dev/vx/rdmp/emc0_X ) and PowerPath device /dev/rhdiskpower.
using AIX default nmon tool to monitor whole traffic on HBA adapter.(nomon --> input letter "a" to check Disk-Adapter-I/O traffic).
customer is testing performance on DMP device and PowerPath one by one ( not DMP+PowerPath co-exist )
from the output of "TOTAL(MB/s)" item ,found value of PowerPath is about two times of DMP.
PowerPath is about 1000MB/s
DMP is about 500-600MB/s so customer considers DMP performance is lower than PowerPath