Internal SSD not showing while booted from external drive

[dood_son]

Ok, so my current approach is to stay with the computer and use the adapter that came with it in order to run a drive that El Capitan will be friends with. A drive that I now need to buy.

1. To use the adapter that I have I need a drive with identical connector as the TOSHIBA THNSN5256GPUK that is currently installed in the computer. That is: M.2 M-key - correct?

2. For a drive to be functional to El Capitan it needs to be AHCI - not NVMe.

3. Still not sure whether the drive has to be SATA or PCIe, or maybe it may be either...?

I have found three SSDs on the web so far. They are:

1. SAMSUNG SM951 MZ-HPV256HDGL
2. SAMSUNG SM951 MZ-HPV2560
3. SAMSUNG PM851 MZ-NTE256D

Are these drives going to work with my mid-2014 MBP 15" as I want them to, that is - through the adapter that came with TOSHIBA THNSN5256GPUK? If they are going to allow me to use El Capitan, can someone please advise on these three drives, which one to choose?

 

[treekram]

Ok, so my current approach is to stay with the computer and use the adapter that came with it in order to run a drive that El Capitan will be friends with. A drive that I now need to buy.

1. To use the adapter that I have I need a drive with identical connector as the TOSHIBA THNSN5256GPUK that is currently installed in the computer. That is: M.2 M-key - correct?

2. For a drive to be functional to El Capitan it needs to be AHCI - not NVMe.

3. Still not sure whether the drive has to be SATA or PCIe, or maybe it may be either...?

I have found three SSDs on the web so far. They are:

1. SAMSUNG SM951 MZ-HPV256HDGL
2. SAMSUNG SM951 MZ-HPV2560
3. SAMSUNG PM851 MZ-NTE256D

Are these drives going to work with my mid-2014 MBP 15" as I want them to, that is - through the adapter that came with TOSHIBA THNSN5256GPUK? If they are going to allow me to use El Capitan, can someone please advise on these three drives, which one to choose?

Do NOT get the PM851. The other two look correct. For me, it would make sense to pay more for a used SSD if it has fewer write/erase cycles. But I rarely see sellers post that information so in this case I don't know why one costs more than the other. On the web and on this forum, people are able to run El Capitan on this SSD.

These SSD's are M.2 PCIe AHCI SSD's. SATA drives will not work in the 2014 MBP. The Toshiba and these Samsung are M-key so the Samsung will fit into the adapter you have.

 

[dood_son]

To all of you who are interested how this ended:

I can confirm that the problem was caused by incompatibility between EL CAPITAN and any NVMe drive. Samsung SM951 works like a magic. The cloning of EL CAPITAN to it went smooth as butter. Pay attention though, that this model was produced in two versions: early ones were AHCI (what you need) and late ones were NVMe. What distinguishes them is the third model letter: H is for AHCI, V is for NVMe.

Thanks again to all who responded!