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I've read a few suggestions that you get worse performance placing the SSD in a caddy in place of the optial drive rather than swapping with the main mechanical.

Is this true?

Can I have my boot drive in the old optical bay, and will I still get SATA II speeds for a supported/ or rather a modern SSD?

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  • I think there are some models of Macs (the 2011 and 2012 MacBook Pros) where the hard drive is SATA III, but the optical drive is still SATA II. That's probably where this advice comes from.
    – benwiggy
    Jan 4, 2020 at 19:55

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You shouldn't get slower speeds because both SATA ports are SATA II (3Gb/s).

You can confirm this by going to About This Mac >> System Report. Then, go down to SATA/SATA Express and select the chipset controlling your optical drive.

(I don't have an optical drive for this example, unfortunately, so mine shows my SSD, but the concept is the same)

Look for Link Speed and Negotiated Link Speed. Link Speed is what the interface is capable of (SATA II/3Gb/s) and Negotiated Link Speed is what the connected device is capable of delivering (SATA I/1.5Gb/s for SuperDrive).

SATA & SATA Express

Provided that both of your SATA ports are SATA II, then the only factor that could slow down the performance would be the caddy; so ensure that you get one that's SATA II or SATA III.

Also, keep in mind that all new SSDs are all SATA III, but they are backward compatible so, even though they are capable of 6Gb/s, the most you'll get is 3Gb/s.

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  • My 2011 iMac shows a Link Speed of 3Gb/s which would not effect the performance if replacing with HDD, but would if replacing with a SSD. Jan 4, 2020 at 20:25
  • @DavidAnderson - how would it affect performance? The fastest you would go is 3Gb/s whether you use a HDD or SSD. You won't get the full performance out of the SSD, but it won't make a difference if you connect your SSD to the optical interface vs the HDD interface; the transfer speed will be the same.
    – Allan
    Jan 4, 2020 at 20:44
  • What do you mean by fastest? Are you referring to the speed data is transferred over the cable or the speed the drive internally operates? I thought SSD operate internally at speeds between 3Gb/s and 6Gb/s. Jan 4, 2020 at 21:48
  • @DavidAnderson - Fastest Transfer speed "over the cable." That's the *negotiated link speed." The speed your SSD operates at internally has nothing to do with how fast the SATA controller is.
    – Allan
    Jan 4, 2020 at 21:50
  • Would you agree that the transfer speed over the cable should be faster than what the drive is capable of operating at? Jan 4, 2020 at 22:11

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