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It seems to be generally accepted in Ask Ubuntu that the maximum size for a casper-rw file is limited to 4GB, there are many posts that state so.

I recently noticed that syslinux 6.03 now supports EXT and NTFS and wondered if the size of casper-rw persistence files could now exceed 4GB, making a separate casper-rw partition unnecessary.

I opened YUMI-2.0.4.9, selected NTFS format, Ubuntu for distribution and 16.04.3 for ISO. I set persistent file size to 5.5GB and pressed Create.

When that finished, I opted to add another distro, this time 14.04.3 with another 5.5GB casper-rw file.

Both installs booted fine and each reported 5.3GB free space. Multiple casper-rw files, larger than 4GB, were working. Boot time was 1/2 that of some other bootable flash drives, shutdown was also fast. (YUMI boots directly from the Ubuntu iso, making point release persistent upgrades easy).

I copied one of the 5.5GB casper-rw files to a folder on usbdata, (the NTFS partition on a mkusb install), removed the casper-rw partition label from the persistent partition and edited grub.cfg, adding a persistent-path to the folder of the casper-rw file. This did not work, as it does with a FAT32 partition.

I'm thinking that there is something in syslinux that allows it's bootloader to map the large casper-rw file to a virtual partition, hd0,3.

My question is Has anyone else been using casper-rw files greater than 4GB, have you found any problems?

Has anyone been able to put large casper-rw files on an EXT partition? (Less likely to fragment than NTFS). MultiBootUSB for Linux will install syslinux to EXT but persistence has not worked for me.

Has anyone managed to get a casper-rw file greater than 4GB working on a Grub2 type install, (like mkusb)?

  • This is a new question I think, YUMI only added the ability to boot NTFS last March. – C.S.Cameron Sep 3 '17 at 18:21
  • Can you get any casper-rw file to work on an ext filesystem with grub? The persistent-path argument does not seem to take a disk, and the casper-rw file's not found when on ext. – ubfan1 Sep 3 '17 at 20:48
  • I think syslinux has found out how to use casper-rw files larger than 4GB, Can grub be similarly updated? I have not gotten a casper-rw to work on ext4 yet. – C.S.Cameron Sep 3 '17 at 21:08

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