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Released June 2012, Model A1278. Intel processor with Turbo Boost

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Slow write speeds on SSD

So this computer has an SSD: OCZ-VERTEX3 240GB. The write speeds according to black magic does to 240; I have trimm support enabled. It should be around ~500+.

What could be the cause?

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There is a similar post MacBook is slow after upgrading to SSD. The general conclusion was that the hard drive cable may be at fault. They tend to be damaged pretty quickly by the bottom plate of the machine (it rubs up against the cable where the cable routes over the optical drive). You can try booting the drive externally through a USB port to see what speeds you get through a different connection point.

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Yes! The HD SATA cable gets damaged as it rubs along a rough surface of the uppercase. Here's a good writeup on the issue Your Hard Drive Cable Is A Ticking Time Bomb

But, there is a hideous second issue! The cable is often damaged in the process of installing it as people tend to fold (crease it) where the cable bends around the corners. You want nice smooth radius bends using a old BIC pen ink straw as a forming brake to help form the bend.

Here's the needed cable: MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable and heres the guide to put it in MacBook Pro 13" Unibody Mid 2012 Hard Drive Cable Replacement

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I tried with a SATA to USB adapter; it's USB 3.0. I got worse speeds.

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If you have a friend with the same model you can try installing the SSD internally in their machine to see what speeds you get. I still suspect the hard drive cable.

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Could be the hard drive cable that dies every time you sneeze on these 2012 models.

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