Question How to format an exFAT drive so MacOS and Windows can write to it? (Part 2: Did I do it right?)

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HerbertSherbet

HerbertSherbet

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Nov 6, 2019
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I need some help. I have a 5TB portable HDD that I long-formatted into exFAT. My plan is to set this drive up and then format a second drive the same way and use these two drives as a portable backup with one redundancy. I want to be able to freely write to it from Windows computers and Mac computers. (I'm also planning on setting up a semi-automated backup system using FreeFileSync.) From what I've done so far I cannot get Mac computers to recognize it beyond Disk Utility.

I think I have to get the allocation unit size right? I'm not sure what to try next.

fQWdgJB.png
 
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For clarity's sake this is what I followed.
Kurt Lang said:
Jan 26, 2013 12:34 PM in response to macjsus

It's a known issue that, depending on how big the drive is, formatting exFAT in OS X uses too large of block (cluster) size that Windows doesn't like. Format the drive from within Windows with a block size no larger than 1024 and you should be able to use the drive on both platforms.
Click to expand...
I first deleted the volume/partition and then quick formatted it to exFAT with an allocation unit size of 1024. At first I got this error message:
"Virtual Disk Manager - The format operation did not complete because the cluster count is higher than expected."
However when I quick formatted it the same way again it seemed to be successful. I'm putting some files on it now and hope to test it on a Mac soon.
 
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It works! I can read/write to it on a Mac and read/write to it on a Windows 10.
exFAT,
1024 (1KB) allocation unit size,
and I do a long format only on the first time I format so the drive can check itself for any problems. Since I've done a long format already before I made this thread I did a quick format this time.

As a heads up long formatting a 5TB HDD through USB 3.0 will pretty much take a whole day.
 
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So I long formatted the second 5TB drive with exFAT 1024K. I got this error message again, the drive had no name, and the drive appeared to have a volume but when opened would prompt me to format it.
Virtual Disk Manager
The format operation did not complete because the cluster count is higher than expected.
Click to expand...

I'm worried about this. This is supposed to be a backup drive. I don't want any instability. I am only going this route because Mac computers, without third-party software installed to bridge the gap, can't write to the same >2TB drives that Windows 10 can outside of this method. If I had the spare time I'd do another long format. It took at least 14 hours and probably longer. Instead, I just did a quick format and it worked this time. I only did the long format because I wanted the drive to check itself and log the results in S.M.A.R.T. so I could make sure it was okay.

If not for this issue I'd be done. Now I have to hold my breath and make sure that all my files actually get saved. This error only appears the first time and doesn't happen the second time so it seems like it still works and works correctly. When I look this up I don't find anything concrete. I found an official Microsoft page about what the default allocation unit size option does, but it isn't informative about minimums or maximums. I also found two 2015 comments that link to a 2011 Mac help thread similar to what I quoted above.
The spec sheet for exFAT is pretty dense.
https://docs.microsoft.com/en-us/windows/win32/fileio/exfat-specification

I've tried to gleam some information about the drive but I still don't understand if it's okay. There's no bad signs from CrystalDiskInfo but I want to make sure I'm not planting some sort of trap for myself.

Results for "fsutil fsinfo volumeinfo G:"
Max Component Length : 255
File System Name : exFAT
Is ReadWrite
Not Thinly-Provisioned
Preserves Case of filenames
Supports Unicode in filenames
Returns Handle Close Result Information
Supports Encrypted File System


Results for "fsutil fsinfo sectorinfo G:"
LogicalBytesPerSector : 512
PhysicalBytesPerSectorForAtomicity : 4096
PhysicalBytesPerSectorForPerformance : 4096
FileSystemEffectivePhysicalBytesPerSectorForAtomicity : 512
Device Alignment : Aligned (0x000)
Partition alignment on device : Aligned (0x000)
Performs Normal Seeks
Trim Supported
Not DAX capable
Not Thinly-Provisioned


Results for "fsutil fsinfo drivetype G:"
G: - Fixed Drive


Results for "fsutil fsinfo ntfsinfo G:"
A local NTFS volume is required for this operation.


Results for "wmic volume get driveletter,blocksize"
BlockSize DriveLetter
4096 D:
4096
4096 C:
4096 F:
1048576 G:
4096 E:
1024


I cannot understand this last one. 1048576 for drive G? This does not seem right. Drive E is an old hard drive and isn't related.

Here's properties for three things I've saved on it as a test. The only text in the New Text Document.txt file is "New Text Document".
yVLc3t8.png
 
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fzabkar said:
You specified an allocation unit size (cluster size) of 1024K instead of 1024. That's 1024 x 1024 = 1048576 bytes.

As you can see in the third screenshot, the minimum size of a file is 1048576 bytes (size on disk). That's 1 cluster or allocation unit.
Click to expand...
That helps things make more sense.

I can't diagnose this error message but I do feel better about it. Knowing that I've set it to 1mb instead of 1kb is a surprise but it works with Mac computers so I'm pretty happy. I guess I'll test the 512K size since it's the only option I have lower than 1024K and it would save me some space in the long run if it works.

I think I'm done. If anyone can tell me what that error message means then please do. No big deal if not.
 
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