I have an older MacBook Air (Mid 2011) now running High Sierra. I am backing up documents, pics, and videos to an external HD that is formatted in exFAT. I use my MBA and a Lenovo system interchangibly and need files accessible on both, hence exFAT. I noticed size and size on disk in Lenovo to be tremendously different (400 GB takes up 800 GB space for example).

In trying to figure out what was happening, I came across an unusual file system block size on my MacBook, at least as far as I am reading it.

I followed the steps shown on this page What are the sector sizes on Mac OS X?.

[![enter image description here][1]][1]

Apparently the 4096 expected file size is 4194304 instead while the Device Block Size and Allocation Block Size are both 4096.

Could you tell me if I'm reading it correctly, that 4194304 is extremely large? If so, how do I fix it?

Thanks in advance.

  • I accidentally hit submit before adding the screenshot. I'll try to do it now. Essentially the information is in the text.
    – Mike K
    Jan 2, 2018 at 18:22
  • Instead of a screenshot can you please copy/paste directly from Terminal, select the whole block and then click on the {} icon on top of the edit window to ensure that it gets formatted directly? That way the content is accessible through search (and for screenreaders) which will make it easier in the future to find the question if necessary.
    – nohillside
    Jan 2, 2018 at 19:33
  • Js-MacBook-Air:~ aman$ diskutil info / | grep "Block Size" Device Block Size: 4096 Bytes Allocation Block Size: 4096 Bytes Js-MacBook-Air:~ aman$ stat -f %k 131072 Js-MacBook-Air:~ aman$ stat -f %k . 4194304 Js-MacBook-Air:~ aman$
    – Mike K
    Jan 2, 2018 at 19:44
  • Please edit the question directly:-)
    – nohillside
    Jan 2, 2018 at 19:58

1 Answer 1


No, that is not extremely large. The command "stat -f %k ." does not as such give you the block size on disk, but rather it is a guide from the OS to user programs as to how large amounts of data at a time it should transfer to/from disk for optimal performance.

With modern SSDs it is not uncommon for that value to be 4 MB as you indicate, instead of the 4 kB that was a kind of "default value" for many years, and not really observed by user space programs anyway.

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