Can't get more 6K IOPs on Pool

Hi,

I got 4 Enterprise SSD, According to Manufacture docs they can perform 40k IOPS on random write 4K bloks, and i what them to use as SLOGs, BUT.

Here is the problem:

Tests:

Create a pool with 8k block size, add 1 SSD,

random write single thread - ~48Megs - 6K IOPS.

random write 2 threads - ~100Megs - 12K IOPS.

destroy pool

Recreate pool with 2 disk  (as stripe)

random write single thread - ~48Megs - 6K IOPS.

random write 2 threads - ~100Megs - 12K IOPS.

3K IOPS goes to Disk 1 and 3K IOPS goes to Disk 2

Same thing with 3 or 4 disks, single thread pool performance are always the same ~ 6K iops.