Atom NAS & SATA 6.0 Gb/s Controller Performance Test

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SATA 6.0 Gb/s HDDs has been on the market for a period of time, and you might wonder whether these HDDs will make your NAS run faster. I am interested in the topic as well, so I would like to do some tests in our lab today, to compare the performance between of SATA 6.0 Gb/s and SATA 3.0 Gb/s on Atom platform.

Understand the Building Blocks

Like computers, to build a NAS server, you need components including CPU, memory, circuit board, I/O controller and ports. HDD are connected to I/O controller hub, where SATA controller is located. Depending on the SATA controller in the I/O controller hub, the bus speed, i.e. the bandwidth, could be 3.0 Gb/s (SATA rev. 2) or 6.0 Gb/s (SATA rev. 3). You can think of it as highway speed limit.

SATA 3.0 Gb/s & SATA 6.0 Gb/s on Atom Platform

If you are looking for performance, then a NAS server with Atom platform will be a likely candidate. Usually an Atom powered device comes with a chipset, namely ICH9R (I/O Controller Hub), which includes the SATA controller controlling the I/O of hard disks. However, its internal disk data transfer rate is up to 3.0 Gb/s (300 MB/s) only. If you would like to have SATA 6.0 Gb/s support, you have to install an external SATA controller on ICH9R via PCIe interface.

Our experimental devices are based on Atom platform and ICH9R chipset. One equips SATA 3.0 Gb/s support with built-in chipset ICH9R. On the other device, we integrated 88SE9125 SATA controller to provide SATA 6.0 Gb/s bandwidth. All other equipment and configurations are the same – same CPU and same RAM size. Each device carries 4 powerful WD Caviar Black HDDs with SATA 6 Gb/s interface. The HDDs are configured to RAID 0 to bring out the best performance.

Test Units & Environment

The specifications of two experimental devices based on Atom platform are listed below:

Device #1 Device #2
SATA Controller SATA 3.0 Gb/s SATA 6.0 Gb/s
CPU Atom D525 Atom D525
RAM DDR2 1GB DDR2 1GB
Chipset ICH9R ICH9R + 88SE9125
HDD WD2002FAEX x 4
(SATA 6 Gb/s)
WD2002FAEX x 4
(SATA 6 Gb/s)
RAID RAID 0 by 4 drives RAID 0 by 4 drives
  • Network Environment: 1Gbps LAN; MTU 1500; directly connected to the client PC
  • Client PC: Intel Core i5 750 2.67GHz; 4GB DDR3; WD3000HLFS (10K RPM, 300GB) HDD x 2, RAID 0; Intel Gigabit CT; MTU 1500; Windows 7

Test #1 – Windows Upload/Download Performance

Once the two devices are ready, I tested the performance between the two using Robocopy to measure writing & reading speed with Windows File Sharing (SMB) protocol. The test is done on Windows 7. A single 5GB file transfer is done to squeeze out the max transfer speed.

Device #1 Device #2
SATA Controller SATA 3.0 Gb/s SATA 6.0 Gb/s
Windows
Upload
108.30 MB/s 103.81 MB/s
Windows
Download
110.83 MB/s 111.55 MB/s

The result above tells two messages – (1) there’s little difference between the two. (2) the transfer speed (108 MB/s writing and 111 MB/s reading) is really close to the 1Gbps LAN limit.

In reality, the files we transfer on a daily basis are usually a lot of small files, so we did another test of copying many files of small sizes (1MB x 5000 files) in two-way direction – (1) from NAS to PC, and (2) from PC to NAS, to simulate scenario in the real world. The result is as follows:

Device #1 Device #2
SATA Controller SATA 3.0 Gb/s SATA 6.0 Gb/s
Windows
Upload
48.33 MB/s 46.60 MB/s
Windows
Download
66.60 MB/s 64.38 MB/s

As above results shows, you won’t see big difference when transferring small files. What’s more, the figures show that device #1 with SATA 3.0 Gb/s runs even faster than device #2 with SATA 6.0 Gb/s.

Test #2 – Direct Disk I/O Performance

In our NAS performance test, it seems the bottleneck blocking the transfer speed is the 1Gbps LAN limit and the overhead of file sharing protocol. Therefore we should look for scenarios that doesn’t involve these two factors. For example, you might do daily backup of your data from one volume to another, or move the shared folders among different volumes – all of which involves file copy operations between volumes.

Therefore, I did a test on the two devices: (1) Build two RAID 0 volumes, each of which consists two drives. (2) Copy a single file of 50 GB from a RAID 0 volume to another.

Device #1 Device #2
SATA Controller SATA 3.0 Gb/s SATA 6.0 Gb/s
Speed 182.77 MB/s 131.14 MB/s

Since there is no 1Gbps LAN limit bottleneck blocking the transfer speed or overhead of file sharing protocol involved, the figure reflects the maximum speed of direct disk I/O. Surprisingly, as you can see above, device #1 with SATA 3.0 Gb/s performs much better (182 MB/s) compared to Device #2 with SATA 6.0 Gb/s controller (131 MB/s). From the result, it looks like SATA 6.0 Gb/s hasn’t shown its full potential yet. Like many of you who is reading this article, I, too, hope there would be a better solution of NAS supporting SATA 6.0Gb/s before long.

Summary

In theory, SATA 6.0 Gb/s solution should provide better performance than SATA 3.0 Gb/s. However, the result suggests that, substantial performance gain is yet to be observed from using an add-on SATA 6.0 Gb/s controller. We are still considering to adopting SATA 6.0 Gb/s interface in the future, but only when the technology matures and when it show appreciable performance gains. Once the moment arrives, I’m sure we’ll have a product that has SATA 6.0 Gb/s support.