How to observe the Effect of DMP iopolicy with vxdmpadm iostat
Article ID: 100027419
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To set up observation of DMP I/O statistics view the vxprint -ht output and select the volume ("v") that is busy with I/O. Identify the "sd" (subdisks) objects under that "v" volume. Decide which "sd" “device” (e.g. Disk_0, emcpower45, c11t50d0s2) which will be the "dmpnodename" of the device you wish to view I/O statistics. Start the vxdmpadm iostat statistic collection :
# vxdmpadm iostat start
To show the current statistics on all paths.
# vxdmpadm iostat show all
To view statistcs for one specific dmpnodename -
# vxdmpadm iostat show dmpnodename=
Use this command to reset the statistics to zero
# vxdmpadm iostat reset
To simulate input operation on a specific volume, Read from volume for e.g. vol1 :
# dd if=/dev/vx/rdsk/testdg/vol1 of=/dev/null bs=1024 count=2000000000 &
Open another session and display I/O statistics over time, For example display dmp statistics by using pathname, dmpnodename or enclosure name:
# vxdmpadm iostat show pathname=
# vxdmpadm iostat show enclosure=SUN35100
Use this command to stop vxdmpadm statistics gathering.
# vxdmpadm iostat stop
View and change the iopolicy,
Identify the array enclosure name :
# vxdmpadm listenclosure all
ENCLR_NAME ENCLR_TYPE ENCLR_SNO STATUS ARRAY_TYPE LUN_COUNT
===================================================================================
sun35100 SUN3510 004C1E CONNECTED A/A 8
disk Disk DISKS CONNECTED Disk 2
Note the "ENCLR_NAME" for the array and view the current iopolicy
# vxdmpadm getattr enclosure
For example sum35100
# vxdmpadm getattr enclosure sun35100 iopolicy
ENCLR_NAME DEFAULT CURRENT
============================================
sun35100 MinimumQ MinimumQ
To change the iopolicy dynamically depending on the application requirement and determining the suitable I/O policy of minimumq, balanced, round robin etc ->
# vxdmpadm setattr enclosure
If a DMP iopolicy is set to other than the default policy, the policy will be made persistent in the file /etc/vx/dmppolicy.info. The DMP iopolicies are described in VxVM Admin Guide, please review to understand the different I/O policies features and also monitor I/O load status using vxdmpadm iostat to determine which I/O policy will be the most suitable if a performance issue effects the system. On install the default policy is minimumq.
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