Gen 3 Performance on older iMac with USB 2

Hi - I am seeing read throughput of only 19MB/s in a system loaded with 4 x 4TB drives (2 x WD Red, 2 x Seagate), write throughput typically in the 15MB/s range. It is connected vis USB 2 to a late 2009 iMac with 2.8GHz Core i7 CPU, 12 GB DDR3. USB 3 is not an option with this system. Is this typical for a Gen 3 connected via USB 2? Any other data points for me re your USB 2 performance or tips on increasing it?


I was getting around 20MB/sec on my Late2009 iMac with 16GB.

How much data on your unit? Is Time Machine or Spotlight running when you are doing your transfers?

What benchmarker are you using to get your #'s? I use Blackmagic.

Which version of OSX?

Thanks for the feedback. Disabling Spotlight did result in a significant performance boost - from 19MB/s to approx 26 MB/s (Blackmagic). The unit is at approx 40% of max storage capacity and running on OS X Mavericks. Looks like that is the best that I can expect with USB 2. I will disable Spotlight when doing very large transfers in the future. Appreciate your input.

USB 2.0 does have an expected speed of around 19 - 25 MB/s, I think the only way to improve performance would be to see if you can determine a way to install USB 3.0, as that is the only way to get the full USB 3.0 speeds from the GEN 3. If USB 3.0 is not an option, you have hit the bus limitation of USB 2.0, and that is the best performance you can get from your GEN 3.

Drobo Support

Coming from the Gen2 (using Firewire), to Gen3 using USB2 on a Early 2009 Mac Mini I was really pleasantly surprised at how much faster the Gen3 is compared to the Gen2. That it uses all of the available USB2 speed is good news.

Unfortunately I can’t find my speed test figures for the Gen2 to confirm how much faster the Gen3 is.

If you go to the section GEN 3 MAC PERFORMANCE, you can see my performance figures using a Mac Mini 2009 with USB 2. It think they are excellent.

just pasting link for ease of finding: :slight_smile: