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I have read questions here about exFat and its performance on the Mac. I think I can refute the previous answers and am therefore still looking for an answer or solution. But from the beginning:

My setup:

  • A Western Digital Elements 5TB as external hard drive.
  • MacBook Pro 2021
  • Windows laptop (>5 years old)
  • 3.5TB data stored on a NAS

Scenario 1 (Mac on exFat):

I have formatted the external drive with the Mac as exFat. I try to copy the data from the NAS to the external hard drive. After approx. 6 hours of running time, another 9 days are assumed. Only a relatively small amount of data was copied, so the remaining 9 days would probably have been needed. The activity LED on the hard disk also shows very long pauses. This seemed very suspicious to me.

Scenario 2 (Windows on exFat):

The previous data is deleted (not reformatted). I start the copying process. The prognosis is 9 to 10 hours under Windows. I abort after a few hours. A significant part of the data is copied which makes the prediction of 9 to 10 hours seem realistic. The activity LED on the hard disk flashes continuously.

Scenario 3 (Mac on APFS):

I format the external hard disk with the Mac and start the copying process. Forecast: approx. 9 hours remaining time. The activity LED on the hard disk flashes continuously.

Conclusions:

exFat may have its optimisations for SSDs. But it is possible to write to the same disk with the same cable and the same data under Windows significantly faster. (Scenario 1+2)

It is not due to the external hard drive or the additionally required adapter from USB-A to USB-C on the Mac. The hard disk can also be written to with the Mac in 9 hours (Scenario 3).

Hence the question again:

  • Why is exFAT so slow on the Mac?
  • What can I do to make the disk usable for a Windows PC?

Update 2022-01-10:

Here is a small update of my further investigations

Test 1:

Copy 1 file 39.76GB

APFS 5m 54s

exFAT 5m 50s

Test 2:

Copy 13 files 138,92GB

APFS 21m 09s

exFAT 21m 32s

Test 3:

Copy 1.31 TB

APFS 3h 29m 50s

exFAT 3h 30m 45s

Up to this point, both file systems look about equally fast.

Test 4:

Copy entire 3,5TB

APFS <10 hours (exact stop time missed)

exFAT >15 hours (stopped here) only 486GB on external hard drive

The point is completely illogical to me. Here, significantly less was copied than in the previous test with 1.31TB and in a significantly longer time. This means that the speed was slower from the beginning.

Test 5:

Copy entire 3.5TB with Paragon NTFS driver: approx. 9h 30m

Conclusion:

The file systems are about the same speed for small amounts of data (<1.31TB). But something happens between 1.31TB and 3.5TB. Since the tests are very time-consuming and it is quite difficult to time the copying, I would like to stop my tests at this point. The tip with Paragon fits perfectly in my case.

Markus
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    And what was the actual time for the copy? I find that these predictions are wildly inaccurate - especially when it says "1 minute remaining" if I relied on that to boil an egg it would be like concrete. When the copy starts it may say 9 days then completes in much less time, and yes I have drives formatted as FAT... – Solar Mike Jan 06 '22 at 07:16
  • @SolarMike: Perhaps that was not made clear. Of course, after several hours I examined the sum of the copied data to validate the forecast. I would not have written this question if after 6 hours even 2/3 of the data were on the disk. – Markus Jan 06 '22 at 07:38

2 Answers2

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The reason it is slow is that the implementation is not as optimized as it could have been.

A third party exFAT driver for macOS exists that you could try out. I doubt that it has better performance for. It is open-source and can be downloaded for free.

In order to format the disk so it can be used with better performance on both your Windows PC and your Mac, you can try a different file system. If you like exFAT and primarily have smaller files, you might be able to make do with FAT32 which is natively supported by both operating systems.

Alternatively you could format the drive as APFS, which is the native file system on macOS, and then install an APFS for Windows driver on your Windows PC. Note that the linked software is commercial and requires purchasing a license.

Yet another alternative is to format the drive as NTFS, which is the native file system on Windows, and then install an NTFS for macOS driver on your Mac. The NTFS driver that comes with macOS is read-only, so a separate driver is necessary in order to get read/write access. Note that the linked software is commercial and requires purchasing a license.

jksoegaard
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  • Thank you for your serious answer. I have bought a product and am including it in my tests. – Markus Jan 06 '22 at 13:41
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I did some experiment and found out that

a) the exFAT drive in-queue must be filled. Otherwise it would be very slow (down to 100 KB or less!).

b) Instead copy one big list of directories, copy each directory individually (which might be an issue in old days) and it will fill up the queue

I use exFAT WD-Black D10 as output and input from APFS SanDisk 2TB, WD-Black 5TB in MacOS extended and WD-Black 4TB in exFAT. It could take days if you do not run these in parallel. (The D10 can run up to 2xx MB/s under windows copy prices but in Mac it is still about only 70 MB/s, slow but at least not 100 KB/s)

Dennis Ng
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