Originally Posted by managerman
Ok..I know this uncharted territory at this point, but I wanted to share my results/issues so far.
I have a Asus Z87-A MB with 4770k and 4 Samsung 840 Pro 128Gb SSD in a RAID-0. I am using the latest intel Drivers 12.6..
I think I am totally saturating the Intel RAID controller?? I thought I might see better performance...?
Yes, it is new territory, the SATA III RAID 0 performance of more than two SSDs on an Intel SATA III interface with more than two SATA III ports has never been seen before. Frankly, yours is the first benchmark of four SSDs on the Z87 chipset I've ever seen. It is too early to decide if your results are typical or not, but my initial impression is it probably is normal.
I have used several RAID 0 arrays of SSDs in the past, both on SATA II and SATA III, using two SSDs on SATA III, and three and four SSDs on an Intel SATA II interface. I can give you some insight into RAID 0 performance, and some of the other realities of Intel's RAID performance. Keep in mind this applies only to Intel's RAID performance.
First, performance/speed does not scale up perfectly every time another drive is added to a RAID 0 volume. One aspect of performance, like 4K random read speed, does not scale up at all, and it usually goes down a bit compared to a single drive. It is great that the 4K read speed maintained as much speed as it has in your benchmark, the max for a single 840 Pro is ~38MB/s in AS SSD, I've never seen 39MB/s or more.
Next, there seems to be a point where adding more drives to a RAID 0 volume causes any scaling to stop occurring. That is, the increase in performance does not simply add up to a single drive's score, multiplied by the number of drives. Also, the more drives used, the more this effect is seen. The major transition point in my experience was between three and four drives. Your performance has maintained itself very well given four drives, but as you said, this is new territory and we need to see more results before we know what is normal. I would like to see what three of your SSDs scored for comparison.
As a general example, these are the results of two, three, and four Samsung 830 64GB SSDs in RAID 0 on an Intel SATA II chipset board used as an OS volume:
saying that this example is the way all RAID 0 volumes of multiple SSDs will behave, but you can see how the sequential read speed performance of the four drive RAID 0 volume dropped off quite a bit compared to the the three drive volume. You can also see how performance scaling is maintained well in some areas, less so in others, and not at all in one.
You may be saturating the six port Intel SATA III interface as you said, it does not have infinite bandwidth, and we may now be seeing its limitations as we have seen with the Marvell and ASMedia SATA interfaces for a long time.
I imagine you know that the real world maximum speed of a single SATA III SSD on a SATA III port, due to overhead and other factors not being perfect, is ~540MB/s. Simply dividing 6Gb by eight (bits in a byte) does not result in the maximum speed of a SATA III interface.