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Fragment of a discussion from Talk:BeagleBone Black Extracting eMMC contents
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Small update... it has the same file size limit using an ext2 partition. Weird.

There are no file size limits, e.g. by running "ulimit -a".

My only guess now is that the kernel or dd weren't compiled with LFS, e.g. the _FILE_OFFSET_BITS are not correct...

19:53, 2 January 2015

I confirmed this on a rev. C board. The images are limited to 2Gb. I agree that it looks like the save-emmc image was not compiled with large file support. There's a way around it though, I added on-the-fly compression to commands in aurorun.sh:

  1. backup

dd if=/dev/mmcblk1 bs=100M | gzip -c > /mnt/BBB-eMMC-$RANDOM.img.gz >>/mnt/autorun.log 2>&1

  1. restore

gunzip -c /mnt/BBB-stockDebian.revC.img.gz | dd of=/dev/mmcblk1 bs=100M >>/mnt/autorun.log 2>&1

(thanks for the idea to send the output to a log file by they way, this adaptation gets both stdin and stdout) It takes a lot longer: >20 minutes to compress and ~15 to decompress but the resulting stock debian image is 572 megabytes. That's from a 4 gig eMMC that is 42% full. That means that unless you are trying to image an eMMC drive full of compressed movies or images then it should always fit under the 2 gig limit, plus you can fit more images on your SD card.

15:35, 5 January 2015

Thanks for the confirmation! I thought I was going crazy...

I like the fix too. I ended up just booting a full stock image and dd'ing the image that way, but this is probably better. I guess I was kind of worried it wouldn't be able to read past the 2GB limit on mmcblk1 either.

16:12, 6 January 2015

Agreed that the 2GB limit isn't on all FAT partitions, only non-FAT32 partitions. This really isn't an issue with the shared image as I don't provide the format information (which makes it easier to work with non-Linux systems). The work-around of always compressing the images seems practical, so I added it to my image.

Thanks for all your trouble-shooting!

08:34, 6 February 2015

Oh, sorry I just sent you a talk message before I saw your reply here.

Well the current build can't even write files larger than 2GB to ext partitions. I was also able to write a 4GB file to the same SD card and FAT partition (using the stock build or a PC) that this build could only write a 2GB file to, so it almost certainly isn't a filesystem issue.

Almost all FAT partitions nowadays are FAT32 (as older versions can't even make partitions that are larger than 4GB), so it is very unlikely that is the issue either.

It's been a while since I built linux, but it would seem that this is an issue with the kernel build. I would have assumed that large file support was always built in to recent kernels, but perhaps some how it was omitted or broken on this build?

09:47, 6 February 2015