I had similar problem. When moving SSD from one bay (main bay or optical drive bay) to the other bay, it would perform very slowly. The SSD seems to work fine in whichever bay the SSD was in when it was originally installed (whether the main bay or the optical drive bay). It was only when the SSD was moved to the other bay that I began to see highly variable read/write times, which at times were normal [400-500 MB/s ], but most times were very [<100 MB/sec].
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I had similar problem. Macbook Pro 13”, 2011, running Sierra and High Sierra (problem manifests in both versions of OS X)
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When moving SSD from one bay (main bay or optical drive bay) to the other bay, it would perform very slowly. The SSD seems to work fine in whichever bay the SSD was in when it was originally installed (whether the main bay or the optical drive bay). It was only when the SSD was moved to the other bay that I began to see highly variable read/write times, which at times were normal [400-500 MB/s ], but most times were very [<100 MB/sec].
Note: I have tested both my main bay and my optical drive bay, and both are Sata III (I have achieved read/write speeds between 400-500 MB/s on both bays).
I had similar problem. When moving SSD from one bay (main bay or optical drive bay) to the other bay, it would perform very slowly. The SSD seems to work fine in whichever bay the SSD was in when it was originally installed (whether the main bay or the optical drive bay). It was only when the SSD was moved to the other bay that I began to see highly variable read/write times, which at times were normal [400-500 MB/s ], but most times were very [<100 MB/sec].
Note: I have tested both my main bay and my optical drive bay, and both are Sata III (I have achieved read/write speeds between 400-500 MB/s on both bays).
Any Ideas?