Solaris 11 / Oracle Database Performance

We've been battling with very slow performance for some time. Herewith a detail description of the problem:

Solaris-11/ZFS/Oracle problem

We purchased Oracle T4-2 servers, and are experiencing some weird performance problems.

Hardware:
T4-2
2 x 600GB HDD per server
128GB memory per server
2 x dual port QLE2562 FO HBAs
IBM V7000 StorWyse data array
2 x CISCO MDS 9148 fibre optic fabric switches
Software:
Solaris 11.1
MPXIO
Solaris 10 branded local zones
ORACLE 10g Enterprise edition
Project for the oracle user:
user.oracle:100::oracle::process.max-file-descriptor=(basic,8192,deny);process.max-stack-size=(priv,32768,deny);project.max-shm-memory=(priv,21474836480,deny)

We received the first server and wanted to migrate our APPB application system and Oracle 10g Standard Edition database from our SUN T5240 to the T4-2.

T4-2 setup � Disk 0:
Global zone: Solaris 11.1 ( ZFS - whole disk for the root pool)
Local zones: On the Solaris 11 environment we built two branded Solaris 10 zones using an Oracle template provided on the Oracle website - solaris-10u11-sparc.bin.

Our complete database resides on the IBM data array, in UFS LUNs.The UFS LUNs were mounted onto ZFS mount-points in the root partition (/), and then LOFS mounted into the zones.

We started with the Solaris 11.1 environment.

1)After a day or two the performance of the database starts deteriorating rapidly. We then stop the database and reboot the machine. After the reboot the performance level is restored.
2)Another huge deterioration in performance happens when we unmount the V7000 LUNs, and reboot to the alternate Solaris, and re-mount the LUNs.
3)What further compounds the issue is that when we start another the database in the second zone, we see another huge performance degradation.
4)We have logged a call with ORACLE. They requested us to gather information which was analysed by them. They did not find anything wrong with the way ORACLE was installed and the setup of the instances.

On Disk 1 we did a Solaris 10 8/11 (Update 10) installation, which we patched with the April 2013 CPU patchset. In this Solaris 10 global zone we built two native Solaris 10 local zones. The Oracle 10g databases were built in the zones (same configurations settings) not in the global zone, onto UFS LUNs. The database in its entirety lives on the IBM V7000 data array. This works fine.

We then received our next T4-2 server.Loaded it again with Solaris 11.1, and upgraded to ORACLE 12c SE Release 12.1.0.1.0 - 64bit12xxx seeing that Oracle 10 is not certified on Solaris 11. To keep things simple, we built two small databases in the ZFS root pool. The complete system now resides on one disk no UFS LUNs to consider, no Fibre Optic fabric, no CISCO switches, no IBM data array, BUT we get the same problem. The system will run for some time and then slow down drastically. Starting the second database slows the system down abnormally.