MacOS – Slow SSD Performance on iMac

macosssd

I recently replaced my broken SuperDrive with an OCZ Agility 3 120GB SSD with the following specs:

  • 2.5" SATA 6Gb/s
  • SandForce 2281 Controller
  • Read 525Mb/s
  • Write 500Mb/s
  • 85K IOPS

I have an Early-2009 24" iMac (9,1), and I purchased a caddy to place the drive in in order that it can sit where the SuperDrive was.

My iMac has a SATA2 bus, but after connecting the SSD it will only connect at SATA1 speeds. I knew that the SuperDrive used to use this speed, but accepted that it was because is was simply an optical drive that could not push the speeds to saturate a SATA1 controller, so why bother with anything better.

However I expected the SSD to link at the SATA2 speeds that the bus supports.

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I have the latest firmware on the drive itself, and on my Mac, I have reset my PRAM, and I don't know what to do next. Why does the SSD not connect at SATA2?

I accept that I cannot get SATA3 like the drive supports, but some initial testing using a disk speed test tool suggests I am only getting just over 100Mb/s write and 145Mb/s read, which is a mere 20-80% more than the regular drive gets.

I cannot just swap the drives over, as it's not like the MacBook Pros that use 2.5" drives. I have done a lot of Googling that suggested a firmware fix for MacBook Pros solved the same issue on those machines, but no luck for my iMac.

I have just put a normal SATA2 drive into the optical caddy, and it comes up at 3Gb (SATA2) just fine. So it seems it's something about the SSD that it doesn't like. Controller? I wouldn't have thought that it cared what was connected, so long as it was SATA?

Best Answer

Looks like a known problem with the SSD. OCZ has a firmware on their forum that will fix the issue. See the post "Changing SATA speed on your "3" series SSD." in this thread.

This portion of the instructions only applies to OCZ "3" series SSD's - Vertex3, Agility3, and Solid3 - all sizes. Some SATAII motherboards, when used with one of the above drives will downgrade the drive to SATA1 speeds. We find this mostly on Nvidia chipset motherboards for PC and Nvidia chipset based Mac's. To resolve this, we have a tool that will set the link speed to be locked at SATAII and improve performance. This can be reversed when you update your motherboard/system so you can have the full SATAIII speed again.

Installing the firmware involves burning a Linux LiveCD so I hope you have a computer with the optical drive still in.

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