I format a usb storage device partition to exfat

mkfs.exfat /dev/sdc1

For the device to work normally in diferent situations I also need to
set the (dos) partition type to 07 (HPFS/NTFS/exFAT). This type info
will be stored in the partition table (for gpt partitions I have no idea
about the type code OR about where it will be stored).

But what if I format the entire dos device to exfat

mkfs.exfat /dev/sdc

where is the fs type code (07) stored then?

On Sun, 15 Oct 2023 10:40:39 -0400, bad sector wrote:

> I format a usb storage device partition to exfat
>
> mkfs.exfat /dev/sdc1
>
> For the device to work normally in diferent situations I also need to
> set the (dos) partition type to 07 (HPFS/NTFS/exFAT). This type info
> will be stored in the partition table (for gpt partitions I have no idea
> about the type code OR about where it will be stored).
>
> But what if I format the entire dos device to exfat
>
> mkfs.exfat /dev/sdc
>
> where is the fs type code (07) stored then?

It isn't.

More specifically, when you format a filesystem, you only build the
parts of the filesystem that directly relate to the data storage.

You assign /partition type codes/ (like "exfat" or "ext4" or "ntfs")
when you /partition/ the device (typically, using something like
fdisk(8) or cfdisk(8) or gparted(8)).

Since you intend to format the entire device as a single filesystem,
there will be no partition table (either MBR or GPT), and thus no
/partition type code/. The OS that you intend to use the filesystem
with must recognize that the device is not partitioned, and must be
able to natively access the unpartitioned filesystem. This is possible
with Linux, but not necessarily with other operating systems. I
seriously doubt that the OS in an embedded system, that would normally
use exFAT as an exchange filesystem, would recognize such a format.

My advice: partition the device so that there's either a GPT or MBR
partition table, and format the 1st (and likely, only) partition with
exFAT in order to keep the device compatible as an exchange filesystem.

HTH
--
Lew Pitcher
"In Skills We Trust"

On 2023-10-15 16:40, bad sector wrote:
>
> I format a usb storage device partition to exfat
>
> mkfs.exfat /dev/sdc1
>
> For the device to work normally in diferent situations I also need to
> set the (dos) partition type to 07 (HPFS/NTFS/exFAT). This type info
> will be stored in the partition table (for gpt partitions I have no idea
> about the type code OR about where it will be stored).

Same place, partition table.

>
> But what if I format the entire dos device to exfat
>
> mkfs.exfat /dev/sdc
>
> where is the fs type code (07) stored then?

It is not.

--
Cheers,
Carlos E.R.

On 10/15/2023 10:40 AM, bad sector wrote:
>
> I format a usb storage device partition to exfat
>
> mkfs.exfat /dev/sdc1
>
> For the device to work normally in diferent situations I also need to set the (dos) partition type to 07 (HPFS/NTFS/exFAT). This type info will be stored in the partition table (for gpt partitions I have no idea about the type code OR about where it will be stored).
>
> But what if I format the entire dos device to exfat
>
> mkfs.exfat /dev/sdc
>
> where is the fs type code (07) stored then?

Have hex editor, will travel.

On Windows, you use this. When run as Administrator,
this tool has raw disk access and can examine anything.

https://mh-nexus.de/en/hxd/

Google is sadly lacking in info that I can use, about ExFAT.

Of course you can lay down raw file systems, WITHOUT AN MBR.
You can also lay down file systems with an MBR.
Then, it's up to your OS, what happens next.

sudo apt install disktype
sudo disktype /dev/sdc

That means there are at least three cases:

raw file system # what you did
MBR+partition # What Windows might do, no guarantees (MSDOS disk layout)
# Using the "format" command from the shell, might do a raw one.
MBR+protective 0xEE+GPT tables+partition # A GPT disk (sudo gdisk /dev/sdc and check, it sniffs for stuff)

File systems usually have a namestring, which ideally is in
the first sector. If the first sector does not have 0xAA55
at the end or whatever, then it will not be mistaken for an MBR.

For ExFAT, you might see "EXFAT 0x20 0x20 0x20"
for the eight byte field. And it might be in the
second sector. If it were well designed, it would be
in the very first sector. But since no "softie"
article lists info from a hardware perspective,
we're left sucking for oxygen.

starman pcministry doesn't seem to have info on this.
That's a hex editor guy :-) He even buys groceries
with a hex editor, that's how much he uses them.

Paul

On 10/15/23 5:06 PM, Paul wrote:
> On 10/15/2023 10:40 AM, bad sector wrote:
>>
>> I format a usb storage device partition to exfat
>>
>> mkfs.exfat /dev/sdc1
>>
>> For the device to work normally in diferent situations I also need to set the (dos) partition type to 07 (HPFS/NTFS/exFAT). This type info will be stored in the partition table (for gpt partitions I have no idea about the type code OR about where it will be stored).
>>
>> But what if I format the entire dos device to exfat
>>
>> mkfs.exfat /dev/sdc
>>
>> where is the fs type code (07) stored then?
>
> Have hex editor, will travel.
>
> On Windows, you use this. When run as Administrator,
> this tool has raw disk access and can examine anything.
>
> https://mh-nexus.de/en/hxd/

The only woindow I have is 7 in vBox under Suse Leap & TW
but I use it so infrequently that I forget everything. One of these days
it's gonna go ...gone.

> Google is sadly lacking in info that I can use, about ExFAT.
>
> Of course you can lay down raw file systems, WITHOUT AN MBR.
> You can also lay down file systems with an MBR.
> Then, it's up to your OS, what happens next.
>
> sudo apt install disktype
> sudo disktype /dev/sdc

Sundays are AvLinux days so here I could install and use disktype,
it shows "exFAT" on raw disk or on partition if exists

rawdisk example:

# disktype /dev/sdc
--- /dev/sdc
Block device, size 57.80 GiB (62058921984 bytes)
exFAT file system

> That means there are at least three cases:
>
> raw file system # what you did

this one formatted NTFS or exfat bombed on the Mac, nothing detected

> MBR+partition # What Windows might do, no guarantees (MSDOS disk layout)

I did this with fdisk then formatted the partition exfat and the Mac
detects an mp4 on it no problem. So transfers to the wife's Mac will go
the exFAT way onto a formatted dos partition

The same move using NTFS didn't work either

Using 57gb Datatraveler 3.0 sticks

> # Using the "format" command from the shell, might do a raw one.
> MBR+protective 0xEE+GPT tables+partition # A GPT disk (sudo gdisk /dev/sdc and check, it sniffs for stuff)
>
> File systems usually have a namestring, which ideally is in
> the first sector. If the first sector does not have 0xAA55
> at the end or whatever, then it will not be mistaken for an MBR.
>
> For ExFAT, you might see "EXFAT 0x20 0x20 0x20"
> for the eight byte field. And it might be in the
> second sector. If it were well designed, it would be
> in the very first sector. But since no "softie"
> article lists info from a hardware perspective,
> we're left sucking for oxygen.
>
> starman pcministry doesn't seem to have info on this.
> That's a hex editor guy :-) He even buys groceries
> with a hex editor, that's how much he uses them.

:-))

As usual you're indispensable, as usual way over my head too, but if I
poke at it enough I do get something done! Thank you