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SUMMARY: Can format but not populate either a FAT32 or ExFAT 128GB USB memory stick. Copying in files fails when more than 32GB are copied. Can't use NTFS because this stick is designed to work with iPhones and the app will not read NTFS partitions.

DETAILS:

I have a 128GB memory stick which is designed to quickly transfer files between a computer and an iPhone. One end is a USB and the other plugs into the iPhone's lightning port. This particular type is extremely common and looks like a "T" when you unfold it Puanv iPhone Flash Drive 128GB USB 3.0.

While this stick is not especially fast when I copy Windows data to it, the transfer rate to my iPhone is much better than the wireless alternatives.

Normally I'd format a large memory stick or USB drive in NTFS, but the app used to transfer files to my iPhone ("CooDisk") will only handle exFAT and FAT32. I've tried both. For exFAT formatting, I've tried both Windows 7 and 10, and for FAT32 I used a free product from RidgeCrop consulting (I can give you the link if you want).

As with all USB storage devices, my stick is formatted as a single active partition.

I do not have a problem formatting. After formatting, ChkDsk seems happy with both FAT32 and exFAT. The CooDisk app works fine with either. After formatting, all the space is ostensibly available for files.

My problem arises when populating the stick with files. Whenever I get beyond 32GB in total space, I have various problems. Either the copy will fail, or ChkDsk will fail. (After running ChkDsk in 'fix' mode, every file created beyond the 32GB limit will be clobbered.) Interestingly, when I use the DOS copy command with "/v" (verify) it will flag an error for files beyond the 32GB limit, although DOS XCopy with "/v" keeps on going. GUI methods also die at 32GB.

Out of sheer desperation, I wrote a script that uses GNU's cp for Windows. Now I can copy more than 32GB of files and chkdsk flags no errors. However files beyond the 32GB limit end up being filled with binary zeros despite the fact that they appear as they should in a directory or Windows file explorer listing. I have also tried various allocation unit sizes from 4K all the way up to 128K and attempted this with three different Windows OSs (Windows XP, Windows 7, and Windows 10). There is no problem with the first 32GB of files copied to the stick regardless of: whether I use exFAT or FAT32; my method of copying; and my choice of AU size.

Finally, there is nothing in these directories that would bother a FAT32 or exFAT system: (a) file and directory names are short (well under 100 characters); (b) directory nesting is minimal (no more than 5 levels); (c) files are small (nothing close to a GB); and directories have relatively few files (nowhere close to 200, for those of you who recall the old FAT limit of 512 files per directory)

The only platform I haven't yet tried is using an aging MacBook that someone gave to me. I'm not terribly good with Macs, but I would rather not be dependent on it (it's 13 years old, although MacBooks are built like tanks).

Also, is it possible that FAT32 and exFAT don't allow more than 32GB on an active partition (I can find no such limitation documented anywhere, in fact in my experience USB storage devices are always bootable.

I forgot to mention that I have tried 128K. That happened the first time that I tried exFAT. It is the default. (BTW FAT32 with 64K AUs was the formatting when I got the stick. If you look at the Amazon link I posted in my OP, you'll see that the seller says that it is compatible with all Windows machines.)

  • You are using Windows. So Windows does support a FAT32 disk larger than 32 GB. This means while you can write more than 32 GB, you can't use Windows, to acomplish that task. I don't need more information, I already knew that information, my comment was specific to Windows. – Ramhound Jul 12 '19 at 22:32
  • "For exFAT formatting, I've tried both Windows 7 and 10, and for FAT32 I used a free product from RidgeCrop consulting (I can give you the link if you want)." - I miss read this statement. I thought you were using this application to format the drive to exFAT. – Ramhound Jul 12 '19 at 22:37
  • Windows does not support FAT32 partitions larger than 32 GB are not supported per the documentation on cluster size. What Windows will do with a partition larger than 32 GB is likely undefined. Are you sure this 128 GB mass storage device is not a fake? If you format it with NTFS are you able to actually put more than 32 GB worth of data on the drive? – Ramhound Jul 12 '19 at 22:41
  • "Windows does not support FAT32 partitions larger than 32 GB are not supported per the documentation on cluster size. What Windows will do with a partition larger than 32 GB is likely undefined" can you please humour me by quoting the relevant section from your link that supports your conclusion that "what Win does with a [FAT32] partition larger than 32GB is undefined? (P.S.: I already explained why I can't use NTFS) – Raj S. Jul 12 '19 at 22:47
  • I am not asking you to use NTFS permanently. I am asking you to test the drive, to make sure you don't have a fake 128 GB flash drive, this could happen if there was a third-party Amazon seller involved. I linked to the cluster documentation. What cluster size did you select when you created the exFAT partition? Once you confirm the drive is actually a 128 GB flash drive I will submit an answer to your question. You should read the table: Default cluster sizes for FAT32. – Ramhound Jul 12 '19 at 22:51
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I do not have a problem formatting. After formatting, ChkDsk seems happy with both FAT32 and exFAT. The CooDisk app works fine with either. After formatting, all the space is ostensibly available for files.

It is not possible to make a 32 GB FAT32 partition that will be supported by any version of Windows.

If you look at the Amazon link I posted in my OP, you'll see that the seller says that it is compatible with all Windows machines.)

Amazon product descriptions are not curated by Amazon. They can be incorrect and unless reported to Amazon will not be corrected. The product is the question is sold by a third-party but shipped by Amazon.

Based on the behavior you describe, I suspect the device isn't actually 128 GB, which is the reason anything past 32 GB generates write errors.

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You have bought a fake memory stick. It is very common. They will format as FAT32 because FAT32 only uses the bottom of memory for its file allocation tables. They usually wont format as NTFS because that uses more of the drive. Google for 'FakeFlashTest' or watch the 100's of YouTube videos of fake flash memory.

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