Windows 10: USB flash drive --assign drive letter back to dynamic from static

Ive just checked the USB flash drive that gave me problems with the Media Creation Tool. Ive just checked it with the Diskpart instruction and the flash drive is GPT. Do flash drives normally have MBR then? I'm guessing that it may have been the USB flash drive that I once used with Rufus. That would have set up GPT on it. Can you give me a step by step if I need to convert back to MBR...if that's what required. If I can sort the problem out I'll go back to using the Media Creation Tool to create the bootable USB media. Ive searched the net and it says it can be done in Disk management. Ive just checked by right clicking on the unallocated space on the drive. Theres no convert to MBR option on the context menu. There is a tutorial on here that shows how to convert gpt to mbr disk in Windows 10 by Brink. It mentions the clean option that you mentioned with diskpart but it also says to finish with convert mbr command. It doesn't mention anything about creating a primary partition like was mentioned earlier in posts above. Is the tutorial ive just mentioned for removable drives intended for USB flash drives or is that tutorial for something different? Could you link me to the correct tutorial for the procedure if there is one

 

That's as maybe, but I have now confirmed that the Media Creation Tool fails with error code 0x80004005 - 0xA001A if the USB you ask it to use has a gpt partition.





After failure, the USB is left 'unalocated'. You can create a new simple volume using Disk Management to make it accessible again but, critically, its is STILL using a gpt partition layout. Only DISKPART or a tool like MiniTool Partition Wizard can make it MBR again.

The MCT only fails after it has downloaded all the files it needs, verified them and created the media in preparation for copying it to the USB. It is not until this point that it attempts (and fails) to format the USB.

Unfortunately, the MCT cleans up after itself at close, so you have to do the whole download over again next time you run it.

 

Thanks for that Bree..Ive just posted above to let you know that the USB was GPT. The screenshot you show is exactly the one I got. So at least I know now if I sort out that USB flash drive back to what it should be the Media Creation Tool should work again. Like you say...if I try to use the Media Creation Tool again I'm going to have the same problem because its still in GPT format...if Ive understood you correctly. Have a look at my last post mate and Id be grateful if you can guide me through how to put my USB back to the way it should be so that I can use the Media Creation Tool for creating my bootable USB installation media again. Thanks pal Could you link me to the correct tutorial for the procedure if there is one

 

Well, unexpectedly having a gpt USB handy, this is how I used DISKPART....





Marking it 'Active' is only necessary if you are manually going to copy the boot files to it from an ISO, and then only if you need it to boot on a legacy bios system.

PS: I've just noticed I use ntfs, this doesn't matter if you are going to use the MCT again, it wipes the partition and formats it to Fat32. If you are making the boot USB manually, it MUST be formatted with Fat32.

 

Is the tutorial wrong then that I mentioned in above post on here..Its called Convert GPT Disk to MBR Disk in Windows 10. That doesn't involve creating a Primary partition but does mention the clean command and the convert mbr command. It then says Create a New Simple Volume. Does that mean use Disk management to finish the process off Simple Volume, format, fat32 etc?

PS If I was to use your example above..Ideally then you would swap FAT32 where you have typed NTFS. What about the Active command...Would I not type in the Active command at all then or doesn't it matter? (I would be using the Media Creation Tool to do the entire process i.e download the ISO and create the bootable Windows 10 flash drive)

 

There are many ways to convert a USB to mbr, this is the one I find easiest/quickest.

All the MCT wants is a USB with an mbr partition layout and a recognisable partition in it. It doesn't care about anything else - it will rewrite the mbr table to remove any existing partition(s) then create a partition, format it to Fat32 itself and mark the partition it creates as 'Active'. It does have to be mbr though, it will fail at the first hurdle if it finds a gpt partition layout (but not before writing to it and corrupting it).

The ACTIVE command is only required for legacy bios booting. UEFI systems will boot without it. A legacy system (or a UEFI in legacy mode) requires a partition to be marked active before it can recognise it as bootable.

 

If I was to use Convert GPT Disk to MBR Disk in Windows 10 tutorial would that achieve the same thing? That doesn't involve creating a Primary partition but does mention the clean command and the convert mbr command. It then says Create a New Simple Volume. Does that mean use Disk management to finish the process off Simple Volume, format, fat32 etc? I am slightly familiar now with Disk Management having created a Simple Volume a couple of times this week

 

Option Four of that tutorial is basically doing the same thing as I did. The difference is that step 6. (convert mbr) just creates an empty mbr table, so step 7. is needed to create a partition in it and format it. My CREATE PARTITION PRIMARY command creates the mbr table and the partition in one go, but I then need a second command to format it. Two ways to skin a cat, both work.

 

Yeah, Option Four of the tutorial was what I talking about mate. Ive got a better understanding now of how things work now you've been patient enough to explain things to this novice lol. I'm guessing an empty MBR table just means the Unallocated Space visual in Disk Management.. I'm going to forget using Rufus to create the bootable media now. Now you've explained what to do to get MBR back I'll put my USB flash drive back to the way it should be and use the Media Creation Tool for the whole process again as I always have in the past. That's what Ive always done and never had an issue until now. Just for future reference Bree because this has always been the method ive used..if the USB flash drive you are about to use with the Media Creation Tool has on it a previous version of Windows 10 installation Media (i.e the Anniversary Update) is it a waste of time and totally unnecessary to manually format it in Windows before using it with the Media Creation Tool? Someone advised me to do that ages ago even though I know the Media Creation Tool formats it when creating the media. I was told it reduces risks of problems..maybe he was wrong.

 

Hi,

Yes and that's true for anything on that stick really. MCT will format it and all data on it will be overwritten. It creates an installation medium that is bootable for both legacy (BIOS) and UEFI systems.
That said, I've never come across a USB stick that was shipped from the factory using a GPT type partition table. I have seen Rufus change user setting of the partition table type on the fly though making it unsuited for the intended purpose in the past.
You really need to keep an eye on it at times.

Cheers, *Wink

 

Yes, the MBR table starts at the first sector of the drive and contains the information describing (up to) four partitions that are on the rest of the drive - start address, sector size etc. If you create an MBR with no info in it, then Disk Management shows it all as 'unallocated'. That's what diskpart's 'convert mbr' command does, it creates an empty mbr. The mbr is essential, but it is not the partition, it is the index to the partitions.

UEFI's gpt uses a completely different way to index the partitions, that's all.

 

Thanks Very much for all your help in this thread. That's what seems to have happened here. I had used one USB flash drive in the past to try the Rufus method..it must have been this one and it was in GPT format. Bree has helped me get to the bottom of exactly what the problem was

 

Thanks Bree for all your help in getting me to what was the actual root cause of the problem..the GPT partition table. I would never have sussed that out. You've been an absolute star and have guided me patiently all the way. I now have a much better understanding. Many Thanks

 

I just wanted to say Thanks to Bree, Caledon Ken and Fdegrove for all of your help in this thread.. You've all been so helpful with your advice. You guys, along with other knowledgeable members on this site, have also helped me with several other issues in the past . TenForums is always the first place I come to whenever I'm having problems. I'd be lost without you guys and would be left tearing my hair out (whats left of it). Many Thanks..Your assistance, as always, is much appreciated

 

You're welcome, any time.

(I don't have much hair left either, but it's not your fault. I lost it long before finding TenForums *Biggrin)