With RAID 10, you need to have FULL redundancy. 2 Controllers, 4 Disk (2 on each) for it to be fast. Basically duplicate data paths to make it faster.

Why would you want 1 controller with 4 disk? I am assuming you have an LX IBM ServeRAID card right? Meaning one channel. You have the data going to 2 disks first and then the other 2 second. On a single channel this makes it SLOW SLOW on Writes. No matter if you were on Raid 0 or not. Reads, different story, the controller will just ask the drives with the heads closest to get the data.

BTW, I am not talking about vpaths either. Seperate Bus for seperate instance of data. RAID-5 is different, reads and writes are nominal, but seperate arrays on seperate controllers (maybe just channels) in RAID-50, would beat RAID-10 in both reads and writes.

Of course this all changes when you only have one drive per channel, the 3ware stuff IOW.

Think about this, u320 is actually u80 with auto-matic hardware encoding (u160 uses the same type of blackmagic, but fewer tokens) the clocking is still the same. That is why u320 drives work on u160 and u80 channels. When it comes down to it, the scsi channel gets saturated quite easily in the different configs, unless they are designed specifically for the purpose at hand.

Whereas the Seperate Channel for each drive methodology is only limited by the controllers fabric and main IO capability.

Now, if this was SSA, things would be different, from a stand point of stacking rather than saturation, the SSA controller has two ways to access any device at a time... but still serial is still serial.