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External Drive Format

aware

macrumors regular
Original poster
Nov 23, 2012
109
10
Hi, i have an external drive formatted in MS-DOS(FAT) and i'm using the drive to store Apple Photos. I know that Apple Photos requires Mac OS Extended(Journaled) to work, so my question is can i just format my mounted partition to be Mac OS Extended and keep the disk as MS-DOS or do i need to format the disk and mounted partition to be Mac OS Extended? What are the difference between the two?
 

Fishrrman

macrumors Core
Feb 20, 2009
20,206
7,128
For Mac files, you want a Mac format.

For an external drive, HFS+ is the best (regardless of whether or not you're using APFS on your internal boot drive).

In disk utility, you want to ERASE the ENTIRE drive to "Mac OS extended with journaling enabled, GUID partition format".

OF COURSE, YOU MUST BACK UP ANY DATA ON THE DRIVE FIRST!
Anything currently on the drive will be destroyed by the re-format.
 

aware

macrumors regular
Original poster
Nov 23, 2012
109
10
If only my mounted partition is Mac OS Extended while my disk remains as MS-DOS, would there be any problems?
 

KALLT

macrumors 603
Sep 23, 2008
5,149
3,194
What you are asking does not make sense. FAT and HFS+ are both file-system formats. A partition can only have one format. A disk can have multiple partitions of different formats. If the partition has the FAT format, it generally has to be erased and formatted into the HFS+ format.

You might be confusing FAT with the MBR partitioning scheme. Both FAT and HFS+ are compatible with that scheme. You should not use the MBR scheme, if you can avoid it. It is less robust and limits the numbers of partitions you can have to 4. You cannot use ‘encrypted HFS+’ or APFS with MBR either. You generally have to erase and format the disk to switch the scheme (though there are tools that can convert between schemes).
 

hobowankenobi

macrumors 65816
Aug 27, 2015
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The short answer is: yes. (...if you meant mounted drive, not partition)

Try it yourself on another drive...even a small flash drive.

1. Erase the entire drive, format it HFS+
2. Add a partition, format it FAT32 (MSDOS-32)
3. Test, test, test!

When I try this with ExFAT, it does not work (always an error). But with FAT32 (MS-DOS 32), the partition is created and seems stable and fine. Both mount and appear as separate drives on the desktop (as partitions would be expected to do).

Will there be any issues? Dunno. I would also test both partitions a good long while be trusting either to be usefully reliable.

Would I want to put serious or important data on it? Probably not. for important stuff, I would want 2 separate drives.

Screen Shot 2020-10-15 at 4.42.31 PM.png
Screen Shot 2020-10-15 at 4.42.41 PM.png
 
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aware

macrumors regular
Original poster
Nov 23, 2012
109
10
Yes, i meant mounted drive(Although it is written as mounted partition in disk utility). So if i formatted only the mounted drive as Mac OS Extended instead of the entire disk, would it be OK?
 

Fishrrman

macrumors Core
Feb 20, 2009
20,206
7,128
If you want to avoid disasters in the future, re-read the advice I gave you in reply 2 above...
 

lostless

macrumors 6502
Oct 22, 2005
379
25
I was thinking, couldn't you use a HFS plus+ expanding disk image inside a exfat drive. Is your drive exfat and not fat? cause if is not exfat, this method will cause issues when your image becomes larger than 4 gigs partition. Fat can't handle files larger than 4 gigs. Im sure it is as most hard drives come as exfat now. if your drive is exfat, you can create a HFS+ expanding image from disk utility and use that. Its basically a file on your drive, but when opened, it will mount a HFS+ image. Advantage of that is that you can keep the data already on that drive.
The other options is to partition the drive to 2 drives. One Fat that will be read on Mac and PC, and another in HFS+ that will only be read by the Mac.
 

hobowankenobi

macrumors 65816
Aug 27, 2015
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You can either:

1. reformat an existing partition
2. add a partition

Regardless, you must back up all data and assume that any existing partition could be destroyed in the process, and all data along with it. While adding a partition should be nondestructinve...it could go badly.

I have not tested adding a partition to a FAT32 volume on a Mac, only adding partitions to HFS+ drives. I can't say if are specific limitiations or complications.

If you bakcup everything to a second drive first...it does beg the question, why not use two seperate drives?

If you decide to proceed, I would strongly recommend that you still have important data in at least one other location. This is always true and a best practice for ALL important data, as any drive could die at any time. But mixing partitions could very well increase the risk of data loss on either partition, or the entire drive.
 

satcomer

macrumors 604
Feb 19, 2008
7,029
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The Finger Lakes Region
The only reason as a Mac user formats for FAT 32 is so using Boot Camp Windows installer can reformat that drive (partition) to NTFS so Windows can install on that drive/partition!
 
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aware

macrumors regular
Original poster
Nov 23, 2012
109
10
I did a test and formatted the mounted drive(Not the disk) to Mac OS Extended. I tried to put files(Videos) larger than 4GB and it has no problem accepting the files. Why would some said it can't accept files larger than 4GB? I know the general advice is to format the entire disk to Mac OS Extended but i would like to know what are the 'bad effects' of formatting only the mounted drive to run Apple Photos? Any thoughts? Just to clarify, my disk came in MS-DOS(FAT) format and have only 1 partition, not 2 partitions.
 
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lostless

macrumors 6502
Oct 22, 2005
379
25
I said in fat32 The max size of a file is 4 GB. If you formatted the drive as Mac OS extended (HFS+), the limit is no longer there. what i was trying to say is that if you still wanted the disk to be read by windows computers, you can format as exfat, which allows files larger than 4Gb. In that drive you can crate a Mac OS extended disk image. Basically a virtual disk on the drive, that you can mount. But the image is the size of all the files in that image. the disk just treats it as a file, so if you have more than 4gb of data in it, it won’t work with a fat32 drive.
 

aware

macrumors regular
Original poster
Nov 23, 2012
109
10
Since my disk is FAT32 and my mounted drive is HFS+, are you saying windows computer can't read the disk if files in FAT32 is more than 4GB but Mac can still store files larger than 4GB as it is HFS+ mounted drive? The only problem is windows can't read the disk, am i correct?
 

lostless

macrumors 6502
Oct 22, 2005
379
25
I’m confused. How is your disk fat32 but mounted As HFS+? That makes no sense. If you formatted as HFS+, it is no longer fat32. They are exclusive to each other.
Both HFS+ and fat32 are file systems. File systems tells the computer how the data on the disk should be stored. Some file systems allow permissions, some not. Some are easier to corrupt and some offer redundancy to the table of contents. Etc ect. Not every OS can read every file system.
Mac OS can read and write to fat16,32 exfat, APFS and HFS+. It can read only NTFS without additional software.
Windows can read and write to NTFS, fat16/32, exfat. But It can’t read e mac file systems.
There are tons of file systems for cds, dvds ect ect. Linux has its own set of file systems. It’s a rabbit hole to learn them all.
back To what I was saying. You can make a “virtual” disk, called a disk image. That can be mounted separately from the main disk. And it can be formtted to whatever you need. If you have your disk as exfat, the drive can still be read by windows, but it won’t be able to access a Mac disk image. If you don’t need windows or Linux compatibility, just leave your drive as HFS+ and save yourself the headache.
 
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flashy-cat

macrumors regular
Apr 8, 2007
116
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UK
If you're short on time, you can skip the backup as changing the partition type will leave your data intact.
 

hobowankenobi

macrumors 65816
Aug 27, 2015
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Since my disk is FAT32 and my mounted drive is HFS+, are you saying windows computer can't read the disk if files in FAT32 is more than 4GB but Mac can still store files larger than 4GB as it is HFS+ mounted drive? The only problem is windows can't read the disk, am i correct?

Herein lies the problem...we don't ever really format drives. We format partitions, and sometimes volumes (depending on the structure of the file system).

When you "format a drive", what is actually happening is that at least one partition is created, and then that partition is formatted. And that varies by file system HFS+ for example has at least one hidden partition, and one useable, visible partition. Apple uses the term "initialize" not "format", but it is the same thing.

Modern file systems (as laid out nicely above) are complitated, and most have mutiple volumes on a partition, and all of that on a drive.

So...your original question is based on the incorrect idea that a drive itself is somehow formated, and other file systems are somehow layered on top of the original.

The big queston we should have asked early on: What problem are you trying to solve?

Usually, when folks want to use a file system other than HFS+ on a Mac, it is because they need an exteral drive to used with a non-Mac. Why do you want something other than HFS+?
 

aware

macrumors regular
Original poster
Nov 23, 2012
109
10
@lossless In this case, isn't the disk FAT32 and the drive is HSF+, or did i misunderstood something?

Disk.png


Drive.png


@hobowankenobi I'm not solving a problem but just trying to understand the difference between formatting drive vs formatting the entire disk and to know whether there are any cons in only formatting the drive. I used HSF+ as mounting drive to access Apple Photos while kept FAT32 as disk to access other files in windows in the future.
 
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Fishrrman

macrumors Core
Feb 20, 2009
20,206
7,128
I'm gonna say it just one more time, and then I'm done with this thread.

For use with a Mac, REFORMAT THE DRIVE to Mac OS extended with journaling enabled, GUID partition format.

This will SOLVE your problems.
 
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lostless

macrumors 6502
Oct 22, 2005
379
25
You are looking at a menu option. It's not showing you the format of the disk. If you right click on the disk when mounted and get info, it will tell you the format of the the actual drive. What your seeing is the drive and partitions. If you format the top option, it will erase all partitions and make 1 partition with what ever format you want. The bottom ones is the listing of all your partitions. Since you only have 1, it shows only one. You can format either and makes no difference. The drive and partition are all just 1 thing at this point. But if you partitioned the drive, you can individually select the different partitions and format each one to whatever you wanted.
If you formatted the drive as HFS+, Try using in a windows machine. I bet it wont work.
 
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hobowankenobi

macrumors 65816
Aug 27, 2015
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What lostless said.

Those choices (images you shared) are the default options DU has listed, not what the drive and partition are.

And yes, you are trying to solve a possible problem: Using the same drive on a Mac and Win box.

Also: there is a variable to be aware of...DU has changed a bit over the years, so the version of the OS you are working on may change your options. My screenshots are from a box running 10.15.7, and it has features older versions of DU do not have...like formatting a drive APFS and NTFS. It may be that older versions of DU will not create both HFS+ and FAT32 partitions on the same drive. It also worked fine—no errors—on a box running 10.13. I don't have a Mac running an older OS to test.

Separate drives are easiest and most reliable.

If you proceed, test alot before trusting either partition.
 
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aware

macrumors regular
Original poster
Nov 23, 2012
109
10
Thanks for the comments guys. One more question, if my drive is originally FAT32 and i formatted the bottom option instead of the top option to HSF+, my drive becomes HSF+ even though i formatted only the partition and would not cause any problem?
 
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lostless

macrumors 6502
Oct 22, 2005
379
25
Thanks for the comments guys. One more question, if my drive is originally FAT32 and i formatted the bottom option instead of the top option to HSF+, my drive becomes HSF+ even though i formatted only the partition and would not cause any problem?
With only 1 partition, it makes no difference. The only difference is the top option erases the partition table and formats the whole drive as whatever format you select. So if you have more than one partition, the top option will remove all those and leave you with just one. You only have 1 partition, so it really doesnt matter if you erase the partition table or not. Does that make sense?
 

clueless88

macrumors member
Aug 23, 2020
81
20
Are you using the external drive in a mixed environment--both Mac and Windows (or Mac and Linux)?
 

aware

macrumors regular
Original poster
Nov 23, 2012
109
10
@lostless Yes, it does. However, i learned that if the drive is FAT32(MS-DOS 32), Disk Utility won’t allow to add or delete partitions on older Mac OS because it has MBR partition table scheme. This is the only con i guess.

@clueless88 Yes
 
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