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The_Great_Sephiroth
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PostPosted: Fri Oct 30, 2015 2:10 pm    Post subject: exFAT not complete? Reply with quote

I have an interesting issue that cropped up with exFAT formatted devices. Now I know exFAT is a work in progress, but I thought this may be helpful to somebody, or if it is known, somebody could enlighten me as to what I am doing wrong.

I copied an album I bought on Amazon Music to my 64GB flash drive which was formatted in Windows 7 Pro 64bit as exFAT with 4k clusters (block size). I can read it fine in Gentoo/Debian/etc, but I had the album on my Gentoo laptop, so I copied it and pasted it onto the stick. When I put the stick into my F150 (2015, brand-new, loaded, it is not an old setup) it did not see the new album at all. I plugged it into my gaming laptop which runs 7 Pro 64bit. I could see and play the music. Back to the truck and no dice. Back tot he laptop. I moved the album onto my gaming laptop, then back to the stick. This time the F150 saw the music and it worked just fine.

This tells me that Windows is writing something extra onto the filesystem which our FUSE module does not write. I have reproduced this several times. Basically, Linux writes the actual data, but does not write some part of exFAT which Sync needs. Bear in mind that the Sync system in my truck was made by Microsoft, so I assume their exFAT support is complete. In other words, we do it well enough to get data to Windows, but devices which require the exact MS format do not like it.

So, am I doing something wrong or is there something not complete? I am running 1.0.1 as far as the FUSE module goes.
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eccerr0r
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PostPosted: Thu Nov 05, 2015 7:46 pm    Post subject: Reply with quote

Was hoping someone else would pass their 2 cents, but I guess not. My situation isn't exactly the same...

I've found that exfat is kind of broken indeed. I tried to rsync a large directory to a 64G SDXC card and it looks like it succeeded, but when I tried reading it back, the contents didn't change. This looked more like a driver problem but it very well could be a filesystem issue.

When I boot into Windows, it will write to the same SDXC card just fine.

Now that fuse-exfat-1.2.1 is in portage I will have to try it...
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charles17
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PostPosted: Fri Nov 06, 2015 7:43 am    Post subject: Re: exFAT not complete? Reply with quote

The_Great_Sephiroth wrote:
... 64GB flash drive which was formatted in Windows 7 Pro 64bit as exFAT with 4k clusters (block size).

Is there any reason to not reformat the drive with vfat?
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eccerr0r
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PostPosted: Fri Nov 06, 2015 6:54 pm    Post subject: Re: exFAT not complete? Reply with quote

charles17 wrote:
Is there any reason to not reformat the drive with vfat?

Obviously it's worth it to try even if cluster sizes get large (I suppose 16KB isn't too bad), but due to M$ I'm sure there are equipment that will freak out if they see a device larger than 32GB formatted with FAT32. Some of it is due to bugs, some of it is due to assumptions (some boneheaded "if size(partition)>32G then filesystem=exFAT" or "unsigned char sectorbuffer[8192]")...
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The_Great_Sephiroth
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PostPosted: Mon Nov 23, 2015 1:43 pm    Post subject: Reply with quote

I do not want large cluster sizes. Highest I will go is 8k (8192b). The thing is, Linux is writing the data to the disk. Windows CAN see, read, and use the data. Every other embedded device cannot. It is like the data isn't even there. My best guess is that there is some other file-table or something which these embedded devices rely on which is not being written. Windows can work around it, but things which adhere to the exFAT standard cannot. For transferring files between Windows and Linux, it is fine. For everything else, it fails.
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Ant P.
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PostPosted: Mon Nov 23, 2015 5:33 pm    Post subject: Reply with quote

The_Great_Sephiroth wrote:
I do not want large cluster sizes. Highest I will go is 8k (8192b).

So... you want a write amplification factor of 8 instead?
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