Hi Dr Lucky,
I feel I have to clarify this point so that other people in a similar situation don’t have to spend a whole day like I did, trying to find the solution as Google doesn’t tell you easily what the answer is. I too thought I had a faulty SanDisk to start with, but of course in hindsight the SSD was perfect - it was the Macbook Pro firmware!!!
So, I encountered similar problems as described in the other posts, with the SanDisk Ultra Plus 256GB with a Macbook pro mid 2009 (Nvidia chipset).
The problem in this case was that the Marvell controller WAS negotiating to the 3GB speed, however this particular Macbook pro had a buggy firmware update aka the infamous EFI 1.7 (which was supposed to work correctly at 3GB/s, but doesn’t work with quite a few non-Apple, third party drives), so here, the SanDisk SSD disk operation was VERY slow. This 1.7 firmware does not work correctly with a lot of disks, not just SSDs but normal hard drives too, apparently.
The fix is to slow the machine to SSD communications down to 1.5GB/s by downgrading the EFI firmware to 1.6 (the forums make it sound scary as the download image is from an untrusted site), but I followed the links (had nothing much to lose at this stage) and it was a straightforward Follow the Instructions scenario. As soon as the update finished and rebooted, the Ultra Plus worked perfectly!
The only downside is that it is only running at 1.5GB SATA, but it’s still a lot faster than the old 5400 RPM HDD.
So for any others in the same boat, if you’ve got issues with this SSD, it’s most likely the MBP firmware, not the SSD, BUT only for this (old) vintage MBP model.
I couldn’t find the link you mentioned in an earlier post Dr Lucky, so reposting it here:
You can also google the following line to find some relevant sites:
Downgrade EFI firmware to 1.6
I’ll just re-iterate the others’ warnings - running this update on the wrong machine could Brick your MBP as it’s upgrading firmware of the machine at a very low level. You take the risk but you might be rewarded with a good result too, like I was.
My 2009 MBP feels like a new speedy machine after this SSD was installed, even thought it’s running at 1/4 the maximum possible 6GB negotiated bus speed.
Good luck peoples!