I have a BIOS (non-UEFI) machine with Win10 on a 3TB drive. I had to
initially create a 2TB for Windows and a 750G drive for additional data.
All is working fine.

On a 2nd drive I have have Mint Linux and can easily access the 2TB
partition but the 750G data drive shows up in gparted as allocated.

This is not at all important but I'm just curious to know what is going
on. Thanks

philo wrote:
> I have a BIOS (non-UEFI) machine with Win10 on a 3TB drive. I had to
> initially create a 2TB for Windows and a 750G drive for additional data.
> All is working fine.
>
> On a 2nd drive I have have Mint Linux and can easily access the 2TB
> partition but the 750G data drive shows up in gparted as allocated.
>
> This is not at all important but I'm just curious to know what is going
> on. Thanks

sudo gdisk /dev/sda
p q

It will tell you whether the drive is partitioned as a GPT
disk drive or as a legacy drive (with the partition table
in the MBR). I like the presentation style of the command.

The GPT disk is newer, has a primary and backup partition table,
the partition tables are at either end of the disk. You can
have something like 128 partitions or so. The partition tables
in that case, are not in the MBR. The MBR still exists, and
separate details about it ("protective partition") are included.
The protective partition declaration, has no function, but
causes naive older OSes to not ruin the GPT portion of the setup.

The GPT disk, also uses LBA sectors with numbering capability
past a 32 bit number. Legacy MSDOS partitioning, the field
regarding sectors, is only 32 bits, and a 32 bit number describing
512 byte sectors, occupies 2.2TB. That is as much as can be
partitioned, using only the MBR four entry partition table.

OK, so if you allocate a 2TB partition, there is only 0.2TB
remaining that can be partitioned into additional chunks. If
the partition you define, stretches *past* the 2.2TB mark,
doing writes to the straddling partition can *corrupt*
the first partition, via the mechanism of address rollover.
A write to 2.2TB plus one byte, writes the first byte of
sector zero instead. Which destroys key metadata to make the
first partition on the disk work.

Review that disk setup carefully, before wishing for anything.

1) Is the disk GPT ?
That's what that gdisk (instead of fdisk) command is for.

The "gdisk" command, contains the means to tell you whether
you should be using "gdisk" or "fdisk".

2) If it says the disk is "not GPT", then you have to start
worrying about the 2.2TB limit and address rollover. And
whether part of the 750GB partition, is on either side of the
2.2TB mark ("straddling").

3) To protect yourself, partitions should not straddle any
"boundaries". You can, for example, on some older OSes,
have address rollover at the 137GB mark (26 bit addressing
of legacy ATA spec). WinXP Gold (no SP3 installed) could
ruin your 320GB disk for you (the partition straddling 137GB
would have the address rollover issue).

An additional command would be

sudo disktype /dev/sda

which will print out the details of the partitioning scheme.
It will even display the details of a Linuxmint Hybrid ISO.
Using that, you can get a quick idea as to whether anything
sane remains in the 750GB or so portion. That tool scans each
partition for "characteristics", and has the ability to tell
you "four out of five indicators, say this is a FAT32 partition".
Not every partition type is that definitive, and that's a
best case feedback from it.

disktype linuxmint.iso

*******

A diagram of a 3TB disk partitioned as MSDOS,
when it should have been GPT. If you do enough writes
to the second partition, it trashes the first partition.
Note that, "formatting" the second partition may place
metadata in places that causes trashing of the first
partition. Run CHKDSK on the first partition, and
see if the CHKDSK gets really concerned about the mess.

+-----+----------------+-----------------+
| MBR | 2TB partition | 750GB partition |
+-----+----------------+-----------------+
|<---- 2.2TB boundary------>|

If you fill the 750GB partition with files, and the
filling goes past the vertical bar at 2.2TB. that ruins
the beginning of the 2TB partition.

If you align things carefully enough, no problemo.

+-----+---------------------+-----------------+
| MBR | 2.2TB partition | 550GB partition |
+-----+---------------------+-----------------+
|<---- 2.2TB boundary------>|

In this case, Windows cannot mount or access that
second partition, cannot write to it, so there is
no longer a rollover problem.

And no, I don't have a lot of operational experience
with "bad partition choices". Not because I'm good
at this stuff, but once you ruin even one disk, it
tends to limit the amount of further experiments
you will want to run. Testing for corruption,
preparing the test cases, takes a lot of time, so
I have no particular interest in collecting more
trivia on this. Burnt once, moved on, so to speak.

Paul

Thank you for the great explaination.
Since it is indeed not GPT I plan to do absolutely nothing.
It's simply a backup partition and I have no need to access it from Linux.

Your good explaination was what I was really looking for.

I have to real plans to change anything here until support for Win10 finally ends and I will have to replace a few of my BIOS mobos with EUFI to support Win11.

Fwiw: I am testing Win11 now, mainly waiting to see what Android capability looks like.

Paul wrote:
> philo wrote:
>> I have a BIOS (non-UEFI) machine with Win10 on a 3TB drive. I had to
>> initially create a 2TB for Windows and a 750G drive for additional
>> data. All is working fine.
>>
>> On a 2nd drive I have have Mint Linux and can easily access the 2TB
>> partition but the 750G data drive shows up in gparted as allocated.
>>
>> This is not at all important but I'm just curious to know what is
>> going on. Thanks
>
> sudo gdisk /dev/sda
> p
> q

I tried this command too out of curiosity, and I got this:

***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format
in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by
typing 'q' if you don't want to convert your MBR partitions
to GPT format!
**************************************************************

I immediately typed q, but was just wondering what is "wrong" with my
setup. Everything seems to work fine...

NP2 wrote:
> Paul wrote:
>> philo wrote:
>>> I have a BIOS (non-UEFI) machine with Win10 on a 3TB drive. I had to
>>> initially create a 2TB for Windows and a 750G drive for additional
>>> data. All is working fine.
>>>
>>> On a 2nd drive I have have Mint Linux and can easily access the 2TB
>>> partition but the 750G data drive shows up in gparted as allocated.
>>>
>>> This is not at all important but I'm just curious to know what is
>>> going on. Thanks
>>
>> sudo gdisk /dev/sda
>> p
>> q
>
> I tried this command too out of curiosity, and I got this:
>
> ***************************************************************
> Found invalid GPT and valid MBR; converting MBR to GPT format
> in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by
> typing 'q' if you don't want to convert your MBR partitions
> to GPT format!
> **************************************************************
>
> I immediately typed q, but was just wondering what is "wrong" with my
> setup. Everything seems to work fine...
>
>
>
https://www.rodsbooks.com/gdisk/walkthrough.html

"When starting gdisk on a disk with existing MBR or BSD disklabel
partitions and no GPT, the program displays a message surrounded by
asterisks about converting the existing partitions to GPT. This is
intended to scare you away if you launch gdisk on the wrong disk by
accident or if you don't know what you're doing."

On 8/10/2021 8:05 AM, philo wrote:
> I have a BIOS (non-UEFI) machine with Win10 on a 3TB drive. I had to
> initially create a 2TB for Windows and a 750G drive for additional data.
> All is working fine.
>
> On a 2nd drive I have have Mint Linux and can easily access the 2TB
> partition but the 750G data drive shows up in gparted as allocated.
>
> This is not at all important but I'm just curious to know what is going
> on. Thanks

OK, Now I recall how I set the drive up originally.

From the Windows installation a 2TB drive was created.

After the installation I used the Seagate software (made by Acronis) to
create the second partition which as IDed and an Acronis virtual device.

From Windows all is fine but now I see why Linux looks as it as
unallocated. I intend to to NOTHING to the drive from Linux.

philo wrote:
> On 8/10/2021 8:05 AM, philo wrote:
>> I have a BIOS (non-UEFI) machine with Win10 on a 3TB drive. I had to
>> initially create a 2TB for Windows and a 750G drive for additional
>> data. All is working fine.
>>
>> On a 2nd drive I have have Mint Linux and can easily access the 2TB
>> partition but the 750G data drive shows up in gparted as allocated.
>>
>> This is not at all important but I'm just curious to know what is
>> going on. Thanks
>
> OK, Now I recall how I set the drive up originally.
>
> From the Windows installation a 2TB drive was created.
>
> After the installation I used the Seagate software (made by Acronis) to
> create the second partition which as IDed and an Acronis virtual device.
>
>
> From Windows all is fine but now I see why Linux looks as it as
> unallocated. I intend to to NOTHING to the drive from Linux.

OK, so you're using Acronis Capacity Manager.

In Linux, you can use a loopback mount with an offset, and
the offset in sectors, tells Linux how to locate the partition.
This is how you bypass the lack of Linux knowledge about
the Acronis Capacity Manager metadata, by using a direct
Linux mount pointed at a particular offset from the
beginning of the disk drive.

The problem with this, is for some reason I could only
get around a 10MB write rate to the 750GB partition, while
doing that in Linux. It was unclear why the slow speed
was evident.

But yes, before I started using GPT, I was using Acronis Capacity Manager.

Paul

Thanks again Paul.

I really do not need to access that partition from Linux. My real problem was that I forgot how I set it up .

I will leave myself a note on the side of the machine .