Oracle locks up when mirrored on raw lv's

1. writing to mirrored lv takes twice the time compared to writing to non-mirrored lv

AIX'ers!

I wonder: Is it normal that it takes double the time to copy a file from
  scsi disks to ssa disks with sw RAID-1, compared to copying to
non-mirrored ssa disks??
That is my experience, after some tests. I've tried to change attributes
for the lv, I've also tried to enable Fast-Write for Multiple Devices
under smit ssad for some of the ssa disks, but no help.
The problem is that my oracle database is waiting for I/O to complete
writes, and I suspect the sw mirrored ssa disks is responsible for this.
BTW: If I turn the mirror off, Oracle does not complain at all!

I use raw device for the tablespace files, redo log files and control files.

I would be grateful for any response!

Arne S

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