Hello,
I'm currently hosting a game server with the current specification
E1230
32GB Ram
2x 1Tb SATA
Windows 2008 server
SQL Server 2012
Databse size is 10Gb
Number of players 1k

- The problem at first I had I/O bottleneck with 2x1Tb as I was using the default SQL configuration and all the files .mdf and .ldf were stored in default C:/SQLSERVER
- Then I added 2 more 1 Tb disks and I isolated .mdf and .ldf and TempDB locations. Problem has been fixed and I/O is performing well.
- Now I have the opportunity to change the disks system to 4x 300GB SAS in HW RAID 10, the problem I'm limited to 4 Disks 1 Array only, so I will have to store mdf, ldf and tempdb files in the same array and not isolated.
- Will I have I/O issue with this configuration? it will be better than 4x single HDD's which every physical HDD contains mdf, ldf, and tempdb files which I already use at the moment without issue or performance could be worse with shared 4x SAS 300GB RAID 10?

Thank you

It all depends on capabilities of your controller. As you know, the IO performed by kernel threads is only up to the controller, where the latter takes over. With RAID-10 it knows it has at least 3-layered queue (two for mirror and one for stripe). Logically it all bottles down to the controller's cache size, which in turn dictates the size of each queue, plus configuration options if such are available (READ vs WRITE).

Controller is LSI 9260 and the disks are 15k RPM version.