1.5TB External HDD shows in Win7 as EFI Partition, but only in WinOS

^ I presume it is so since Windows does not see any file system and no drive letter assigned.. I also noticed now that the OP has two partitions in Disk 0 too 102.45 GB and 7.91 GB with no file system. All show free space. But I think the OP can mount all these on Linux. Atleast that is what I have understood- rightly or wrongly.:)

jumanji said:

Basically there is something suspicious about your Disk 3.

My observations:

1.If it is a GPT drive, Windows Disk Management will not show the 128MB MSR partition.Here it shows up in WDM as an unallocated partition. ( In comparison look at your Disk 1, the 3TB drive, which you say is a GPT drive. It does not show the 128 MB MSR partition.) Note: The 128 MB MSR partition can be seen in Partition Wizard and AOMEI Partition Assistant as 'others" but not as unallocated.

So since that 128 MB is showing in WDM, does that mean that it is not a GPT drive?

jumanji said:

2. Also an external drive initialised as a GPT and formatted with Windows or any partitioning software such as AOMEI Partition Assistant or Partition Wizard will not show the main partition as EFI system Partition.

To me it looks like that the HDD itself was a system drive earlier on an EFI system and you have put that drive now in an external casing.

To my knowledge (best I can remember), there has never been an attempt to install an OS on the drive, nor was it ever (intentionally) partitioned.

Please give the complete history of your Disk 3 including any and all formatting done earlier on that drive , and its component parts. Make, model No. manufacturer and whether it is a branded drive or consists of an external casing where you have put an HDD and made it an external drive and if so its past history.

The drive is a 1.5TB Western Digital green drive, the exact same as this WD 1.5TB SATA 3.5-inch Hard Drive - WD15EARS
The HDD is housed in a nice aluminum enclosure...

jumanji said:

Don't hurry and attempt of converting GPT to MBR without finding the root cause why your Disk 3 appears like this. You may lose all data in it, especially the tutorial suggested by bigmck. Quote from that tutorial "Before you convert a disk, be sure to backup anything that you do not want to lose on that disk. Converting the disk requires that all partitions and volumes are deleted on the disk first." - unquote.

(One can use AOMEI Partition Assistant or MiniTool Partition Wizard to convert from GPT to MBR and viceversa without data loss but in this case of suspicion/mystery I would hesitate to do that without backing up the data on it..)

As whs suggested in a previous post, it would be better if you can copy all data to another drive and format the drive in Windows the way you want instead of trying to untangle this mystery and set it right. It can perhaps be done but it may be a laborious process involving long investigative procedures.

I can be patient for now, because it at least still works in Linux...

jumanji said:

Edit: I also understand that Linux can format external drives as bootable drives. Hence creation of a bootable EFI system partition cannot be ruled out. In such a case it could well be that Windows will not recognise an external drive that is bootable having a EFI system partition.So a mix of Linux and Windows with drives formatted in Linux may be unreadable by Windows.

The thing to remember, is that only a week ago this same drive had no problem working in either Windows or Linux. This problem arose shortly after installing Linux Peppermint as a dual-boot setup with Windows 7, but I'm certain that I did not accidentally partition the drive during that installation.

The only thing I can think of that could have caused a problem, is that I think I might have accidentally set the BIOS to try to boot off this drive, instead of off the flash drive which was what I had meant to do... I'm not 100% sure that I actually made this error, but I do remember having to fiddle with the boot options more than once...

jumanji said:

EDIT: Please upload any screenshots to Seven Forums servers instead of third party servers.

Will do... My apologies...

jumanji said:

^ I presume it is so since Windows does not see any file system and no drive letter assigned.. I also noticed now that the OP has two partitions in Disk 0 too 102.45 GB and 7.91 GB with no file system. All show free space. But I think the OP can mount all these on Linux. Atleast that is what I have understood- rightly or wrongly.:)

I think the 102 GB is for the Peppermint OS, and the other 8 GB is the swap partition for that OS.

jumanji said:

"So since that 128 MB is showing in WDM, does that mean that it is not a GPT drive?"

That was a good question and here is the answer.

When a drive is initialised as GPT and formatted, Windows creates a 128 MB MSR partition but that will not be visible in Windows Disk Management. AOMEI Partition assistant as well as Partition Wizard will however show that MSR partition as "other".I had also said that using these two partitioning software one can nondestructively (without data loss) convert the drive from GPT to MBR. When that is done that 128 MB MSR partition will become unallocated. It can be seen as Unallocated in Windows Disk Management too now.When again you convert the same drive from MBR to GPT, ahoy!,it does become a GPT drive but the 128MB unallocated space will still remain as unallocated.

So the answer is it can still be a GPT drive. But what is evident is that some sort of conversion has taken place in your external drive/ the 1.5TB WD Green drive at some point of time as a result of which it now shows the 128 MB erstwhile MSR partition as unallocated.

I rightly guessed that your external drive could in fact be be a third party enclosure into which you have put a desktop drive.You have now admitted that :).Would Linux installed on some other drive make your external drive into EFI System drive? I think there are many gaps in your story.That is why it is suspicious and mysterious. :)

I don't know what those "gaps" might be... It was working in both Windows and Linux only about 8 days ago...

jumanji said:

I still do not know the history of that 1.5TB WD Green drive. What is the necessity of a 1.5TB drive to be initialised as a GPT drive? Did you buy it new?Wherefrom did it come?

I bought the drive new from amazon... It has been housed in a metal Nexstar enclosure ever since I bought it about 5 years ago... Like I said, as best as I can recall, I never attempted to put any OS on that drive, nor did I ever intentionally partition the drive...

As I also stated previously, it's only been about a week since the HDD was last known to be fully functional in both Linux and Windows' OS...

While preparing to install the Linux OS, I think I might have accidentally set the drive in question to be the #1 Boot Option in the BIOS screen... I corrected that error right away and set BIOS to boot off the thumb-drive, which was what I had originally intended, the 1.5TB is no longer listed as a boot option.... But do you think that simply telling the system to attempt to boot off of that drive, could that have caused the drive to be changed, or to be viewed different by the system?

jumanji said:

I know that this discussion is not going to resolve your query as to how to get the main partition recognised by Windows. You asked a question and I have answered :)

Now answer my question. I do not know anything Linux.

Your system drive must have been all NTFS before you started installing Linux. You installed Peppermint. Why does it now show two partitions without any file system in Windows? ( Yes I knew that it was Linux swap/ Solaris and Linux - sda5 and sda6 - from your Linux screenshot. In my post#12, I was only answering to whs inviting his attention that just like your enclosure +1.5TB drive in it, you also have two partitions in your system drive which Windows shows as 100% free. No file system recognised by Windows, no drive letter - and it does not mean it is really empty :))

I appreciate you taking the time to explain some of this to me, sorry I kinda made you repeat yourself...

I went ahead and downloaded the free edition of MiniTool Partition Wizard...

Do you think that it would work if I just formatted the 128MB partition on that drive? Or do you think I should go ahead and try to convert the whole drive from GPT to MBR?

None of it.

Since Linux sees your external drive and all data in it, your best option now will be to backup all data to another drive and then format the drive with Windows.. You can wait till you are able to do it.

For the present just run Partition Wizard, take the screenshot of how your external drive looks in it and post it. - the very first screen after you launch the application. After taking the screenshot close Partition Wizard. We can see whether it is really a GPT drive. Don't do anything else.

It's definitely listed as a GPT Volume... And you were right about using the forum's uploader instead of photobucket, it looks much better anyway.

OK, I have seen your post but will take sometime to come up with further instructions.( Right now I am busy with other things.) Don't do anything till I return.