[OSGeoLive] Disk (ISO) size limitations

[edgar.soldin at web.de]

On 05.01.2021 18:31, Angelos Tzotsos wrote:
> Lets re-cap:
>
> We are currently using an iso format for our live system. This is an image file with an embeded iso9660 file system. The length of a file's extent on disc is stored in a 32 bit value, it allows for a maximum length of just over 4.2 GB (more precisely, one byte less than 4 GiB).

well initially you pointed to a page where it said Fat32 max. file size when putting the files (incl. the squashfs img) on a usb stick is the problem. but ok, let's see

>From Wikipedia: "It is possible to circumvent this limitation by using the multi-extent (fragmentation) feature of ISO 9660 Level 3 to create ISO 9660 file systems and single files up to 8 TiB. With this, files larger than 4 GiB can be split up into multiple extents (sequential series of sectors), each not exceeding the 4 GiB limit."

man page of mkisofs says it supports level 3

"
-iso-level level
Set the iso9660 conformance level. Valid numbers are 1..3 and 4.
With level 1, files may only consist of one section and filenames are restricted to 8.3 characters.
With level 2, files may only consist of one section.
With level 3, no restrictions (other than ISO-9660:1988) do apply.
"

> Our problem is that the live system is a squashfs single file (included in the iso9660 file system) that goes over 4GiB often.

i am not deeply familiar with live cd creation but i would assume that there is also a way to format the ISO as UDF instead (allowing larger files/images) or am i wrong?

> Now Ventoy supports iso files larger than 4GiB and can boot them from USBs with filesystems other than FAT. This solves another problem, storing an iso file (>4GiB) on a USB file system. Ventoy does not solve the problem of splitting the squashfs file into several smaller ones so they fit into the iso9660 filesystem.
>
> In any case, Ventoy looks like a great tool for storing multiple iso files on a large USB drive and being able to boot them up directly.

it is. indeed. ..ede