Implications of 100% utilization on dm device
Solution 1:
Experiments seem to confirm that the time spent by the kernel waiting for a sync write to complete is counted against busy%.
So the workload of this particular application (DB2 with the synchronous audit log) was doing:
- open(O_SYNC)
- write()
- close()
to the audit log on every audited activity. Which KILLED performance.
Solution 2:
Everything with your DM setup seems to be fine, also the iostat output looks totally sane. 1500 IOPS are next to nothing for DM and peanuts load for the XIV. You need to look somewhere else.