Mirror slower than primary

[Victor Vitug]

I have an Oracle OPC two node setup and the data is in shared drives. The drives were organized in pairs to match RPM and size. Raw logical volumes were created and mirrored on each pair for Oracle.

Using SAR -d I find that the primary disk was busied than the mirror and the mirror had significantly longer wait (2x or more) times (avque, await, avserv). I checked Glance Plus on the LVM activity and found that the slow pairs were mostly read. While the pairs with write and read had relatively close stats.
All mirrored pairs were set for parallel synch and NOMWC.

Is it the read that causes this performance difference?
Is there a setting so that the read would be done on the less busy mirrored drive?

I have attached a table from SAR showing these stats. The drives are organised in pairs. Primary is on top. The last two pairs are for the rollbacks and archivelogs.