Question Can't boot from selected drive in boot-up, need help to explain how PC decides on boot device.

Jun 16, 2020
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I have 4 hard drive:
C: WD40TB current boot up device
D: SG20TB (bootable device because it used to be my C: drive)
E: WD20TB my data drive

The drive "E" above had been acting up, so I bought a new 40TB drive (will call it WD40TB-2 here). I thought it would be a simple matter of taking out the "E" drive above, and install the new drive in the same slot with the same cables, which was what I did this morning. Well, to my total surprise, my PC boots up with the "D" drive above. I re-started my PC and interrupted the bootup, selected to boot from "WD40TB". Well, it didn't matter, the PC still booted with the SG20TB. I repeated this multiple times and kept getting the same results. Finally, I removed the new drive and put back the "WD20TB" (i.e. the original "E" drive). Sure enough, it now boot with the WD40TB, just the way it was before.

Can anyone understand what I did wrong, what do I need to do in order to boot from WD40TB like before (but with the new drive replacing the WD20TB)?
 

R_1

Glorious
Ambassador
Welcome to the forums :D

Did you have both C and E installed when you installed windows?
Windows likes to put needed boot files on other drives during install, its an attempt to save SSD space, when this happen both drives are now needed to boot windows. there is a partition on the E: that windows needs to boot into C:. when you removed the E: the C: became unbootable and the system attempted to boot the other drive, which is bootable by itself.
 
Jun 16, 2020
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Welcome to the forums :D

Did you have both C and E installed when you installed windows?
Windows likes to put needed boot files on other drives during install, its an attempt to save SSD space, when this happen both drives are now needed to boot windows. there is a partition on the E: that windows needs to boot into C:. when you removed the E: the C: became unbootable and the system attempted to boot the other drive, which is bootable by itself.
Thank you for the quick reply.
I believe I had both D and E already installed when I added the now C drive. What's interesting is that I had removed all data from E and reformatted E, so C must not have dependencies on E to boot. This is really strange!
 

USAFRet

Titan
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Mar 16, 2013
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Thank you for the quick reply.
I believe I had both D and E already installed when I added the now C drive. What's interesting is that I had removed all data from E and reformatted E, so C must not have dependencies on E to boot. This is really strange!
Reformatting that E partition did not remove the small boot partition.
 
Jun 16, 2020
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This is going to sound stupid ..... I couldn't figure out how to insert a picture. The insert picture option pops up a prompt for an URL.
 
Jun 16, 2020
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Maybe this can work:

Disk 0 (Basic, 3726.02 GB Online)(C:) 2047.51 GB NTFS, Healthy (Boot, Page File, Crash Dump, Primary Partition)495 MB Health (Reocvery Patitiion)1678.02 GB Unallocated
Disk 1 (Basic 1863.02 GB Online)(D:) 1861.63 GB NTFS, Healthy (Primary Partition)100MB Healthy (EFI System Partition)872MB450 MB Healthy (Recovery Partition)
Disk 2 (Basic 1863.02 GB Online)101MB Unallocated(E:) 1862.92 GB NTFS, Healthy (System, Active, Primary Partition)
 
Your system boots from drive E: . "System" in the description means, the drive contains active bootloader.

Your 4TB drive is unbootable. It doesn't contain bootloader. Also your 4TB drive has improper partitioning scheme. Usable space on the drive is limited to 2TB. Rest of the drive capacity is unavailable because of improper partitioning scheme being used.
 
Jun 16, 2020
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For the E drive, I reformatted it, so I'm surprised that it's still bootable (I just checked and confirmed there's no files I can see). Anyway, I don't really care about that drive anyway, will be throwing it out.

the 4TB drive is what I'm booting from, so it's definitely bootable. I'm aware that only half the capacity is usable, as I didn't know the 2TB limit at the time when I installed Win10. My plan was to (later) get an SSD to clone this drive so that I will boot from the SSD and convert this 4TB drive to GPT to utilize the whole 4TB .... but this plan won't work if the C drive relies on boot info resided on another drive.
 
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USAFRet

Titan
Moderator
Mar 16, 2013
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For the E drive, I reformatted it, so I'm surprised that it's still bootable (I just checked and confirmed there's no files I can see). Anyway, I don't really care about that drive anyway, will be throwing it out.
As noted above, just formatting the "E" is NOT formatting that whole physical drive.
It did NOT format the boot partition. Which is what the system is booting from, and then it turns things over to the drive with Windows on it.
Yes, that's the way it works.
 

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