0

The maximum number of clusters allowed under FAT32 is about 268,435,455 (2^28). A 250GB partition requires 488,397,168 512-byte sectors, which with a 1K cluster size would mean about 243,245,000 clusters, way below the FAT32 limit. But you can't do it!

Why do I have to use at least a 2K cluster size instead?

Related thread: Why is FAT32 limited to just under 2^28 clusters?

4
  • What are you using to format the partition?
    – plugwash
    Commented Jan 16, 2022 at 4:09
  • I was going to ask the same. Windows formatting tools, expecially for FAT32 are pretty terrible
    – Journeyman Geek
    Commented Jan 16, 2022 at 4:16
  • See superuser.com/questions/465615/…
    – sawdust
    Commented Jan 16, 2022 at 23:37
  • I've used AOMEI Partition Assistant. I also have an older version of Acronis Disk Directory (2011), that one let's me do with 1K cluster but the resulting file system is only 135GB on the 250GB partition, which suggests they had a bug allowing 1K cluster size against some other FAT32 limit that I do not understand. Commented Jan 17, 2022 at 5:12

2 Answers 2

0

The purpose of this answer is to counter the following comment from the OP [emphasis mine]:

Even with 3rd party tools, I am forced to use a 2K cluster size with FAT32 on a 250GB volume. I do not understand why that is, why no tool can do it with 1K clusters given the FAT32 limit as I understand it.

Testbed

$ cat /etc/issue
Ubuntu 21.10 \n \l

$ uname -a
Linux xxxxxx 5.13.0-20-generic #20-Ubuntu SMP Fri Oct 15 14:21:35 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

$ mkfs.fat 2>/dev/null
mkfs.fat 4.2 (2021-01-31)
No device specified.

Preparation

$ truncate -s 250G filesystem

$ wc -c filesystem 
268435456000 filesystem

(Note 250G means 250 GiB which is even bigger than 250 GB you had in mind. I have tested both sizes. This answer shows just one test for brevity.)

Filesystem creation

Deliberate attempt with cluster size of 512 bytes, to see what happens when the cluster size is really too small:

$ mkfs.fat -F 32 -S 512 -s 1 -v filesystem
mkfs.fat 4.2 (2021-01-31)
WARNING: Number of clusters for 32 bit FAT is less then suggested minimum.
mkfs.fat: Not enough or too many clusters for filesystem - try less or more sectors per cluster

With cluster size of 1024 bytes:

$ mkfs.fat -F 32 -S 512 -s 2 -v filesystem
mkfs.fat 4.2 (2021-01-31)
filesystem has 255 heads and 63 sectors per track,
hidden sectors 0x0000;
logical sector size is 512,
using 0xf8 media descriptor, with 524287953 sectors;
drive number 0x80;
filesystem has 2 32-bit FATs and 2 sectors per cluster.
FAT size is 2032124 sectors, and provides 260111836 clusters.
There are 32 reserved sectors.
Volume ID is 46a16c4f, no volume label.

$ echo $?
0

Verification

$ file filesystem
filesystem: DOS/MBR boot sector, code offset 0x58+2, OEM-ID "mkfs.fat", sectors/cluster 2, Media descriptor 0xf8, sectors/track 63, heads 255, FAT (32 bit), sectors/FAT 2032124, serial number 0x46a16c4f, unlabeled

$ sudo mount filesystem /mnt/tmp

$ echo $?
0

Conclusions

The 3rd party tools you tried may be arbitrarily limited (like Windows, possibly to a smaller degree but still). The claim "no tool can do it with 1K clusters" is unjustified, mkfs.fat in Linux can.

1
  • That settles it---there is no real limitation preventing it. I'll just have to do it this way through Linux. Thank you so much! Commented Jan 18, 2022 at 10:02
2

Essentially - the formatting tools on modern versions of windows are 'worse' that those of win 9x versions, and tend to give you limited options. I've created a 250gb partition in a VHD

Windows won't even let you format the disk as FAT to start with in the disk management MMC - I think it follows the 32GB maximum windows arbitrarily has on all NT family systems.

enter image description here

Or anything but NTFS in windows 11

enter image description here

(I've tested it in windows 10 too. I don't think I have anything older in the farm)

However using a third party formatting tool - I favour ridgecrop's fat32 formatter, and in this case I used the GUI version

enter image description here

Fundamentally - this is a limitation of the windows disk formatter. Amusingly enough, while its almost always impossible to know what a developer was thinking in making decisions like this, the person who wrote the UI of the original version has a youtube video about the disk formatter which explains the reasoning behind this - which boils down to "I didn't think that anyone would need a drive bigger than 32Gb in FAT32 for the life of NT4.0, someone would replace it."

3
  • 1
    Unbelievable. Thanks for posting the link to the video!
    – r2d3
    Commented Jan 16, 2022 at 9:35
  • I know Windows doesn't allow FAT32 at all above 32GB volume size, and the reason for it is history. But that didn't answer the question, which had nothing to do with Windows. Even with 3rd party tools, I am forced to use a 2K cluster size with FAT32 on a 250GB volume. I do not understand why that is, why no tool can do it with 1K clusters given the FAT32 limit as I understand it. Commented Jan 17, 2022 at 5:07
  • Uh.. the third party tool I used managed to do it. (ignore the cluster size on the dropdown, its the default). Kamil's answer shows it can be done on another OS as well. So fundamentally ... you can? With the right tool?
    – Journeyman Geek
    Commented Jan 17, 2022 at 8:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .