How do I fix a drive letter issue after doing a startup repair?

This old thread may explain some of what is involved Converting a dynamic disk to basic without data loss

We have a Tutorial for this ...
Convert a Dynamic Disk to a Basic Disk

There was also information on the link I posted above about changing a setting to make the dynamic disk visible or more precicely revert to a standard disk by manually editing the MBR - Converting a dynamic disk to basic without data loss

Although, as you have data visible on the disk you may want to try one of the numerous free programs that purport to do the conversion without loss of data first

The one suggested in the tutorial no longer offers this in the free version but a quick google should find a few options ( I have the Paid version of Partition Wizard so cannot recommend any particular program) but as you have your backup it should be OK even if it does not retain data

Barman58 said:

We have a Tutorial for this ...
Convert a Dynamic Disk to a Basic Disk

There was also information on the link I posted above about changing a setting to make the dynamic disk visible or more precicely revert to a standard disk by manually editing the MBR - Converting a dynamic disk to basic without data loss

Although, as you have data visible on the disk you may want to try one of the numerous free programs that purport to do the conversion without loss of data first

The one suggested in the tutorial no longer offers this in the free version but a quick google should find a few options ( I have the Paid version of Partition Wizard so cannot recommend any particular program) but as you have your backup it should be OK even if it does not retain data

Actually, what I'd like to do now is switch out the D: drive with a new, bigger HDD drive. I can do the data recovery to it later.

In fact, this is what it looks like after installing the new drive. Notice I haven't done anything to it other than physically putting it into it's new slot.

The boot partition and C: are still set to Disk 1 and not Disk 0 like before. I don't think it will let me change it.

So the situation is different, now. What would I need to do in this particular case?

What happened? Post #1 showed a pic that included: ( D: ) 100 MB NTFS Healthy (Active, Primary)
That was the D, that was the partition I suggested dropped the drive letter from. Is that not the partition used by Windows 7 to boot and load? I just now noticed: that particular partition was on Disk 1, not on Disk 0. How did a Windows boot/load partition did onto Disk 1 and not be on Disk 0?

The disk numbers are set by the physical location, assuming you have Six SATA ports on the motherboard numbered One to Six the the drive plugged into the first port, (Port One) will show up as Disk 0. This is based on windows which starts numbering disks from 0, (some other applications e.g.. Partition Wizard actually start numbering from 1 so would show a different number from Windows own Disk Management).

So basically if you wish to have your System drive showing as Drive 0, the first drive, you need to physically connect the SATA connections to the drives in the order you want. (this will not actually make any difference to the running of the system but I will admit it's slightly easier on the user if the drives are in an order that is logical)

Yes laptops can limit your options.
You could disconnect the existing Drive 0 and reconnect to the other SATA connection and then add the new drive to the freed up connector, ( if they will fit), which should show the windows drive as Drive 0 and the new drive as Drive 1 but as It will work the same which ever order they show in the drive management so it's just personal choice.

The only prep you should need for the new drive 0 is to ensure it is partitioned how you want it. The default would be a single partition, and that it it formatted, normally these days the default is NTFS. For general use for data storage these defaults are fine. There is also the question of the low level files system MBR or GPT - for a data drive I would simply use what ever is on the drive as default - unless you wish to use it to run multiple Operating systems or the drive is larger than 2TB and you wish to utilise a single partition, (with large drives the GPT system is normally used to present the drive as a single partition as it sells Drives)

Yes that order seems fine :)