[OSGeoLive] Disk (ISO) size limitations

[Angelos Tzotsos]

Hi,

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

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.

Best,
Angelos


On 12/28/20 7:49 PM, edgar.soldin at web.de wrote:
> hey All, Angelos,
>
> incidentally i just came across Ventoy[1] via the Qemu Advent Calendar[2], a usb stick boot manager that boots ISOs from an otherwise usable data partition. it supports exFat, NTFS (to name cross platform candidates) among others so there is actually no 4GB file size limit.
> just booted osgeolive-14.0alpha3-amd64.iso with Ventoy 1.0.31.
>
> where there is a will, there is fun - to be had.. ede
>
> [1] https://www.ventoy.net/en/doc_start.html
> [2] https://qemu-advent-calendar.org/
>
> On 17.12.2020 12:30, Angelos Tzotsos wrote:
>> Hi,
>>
>> The limitation is not actually the iso format but the squashfs filesystem for the live system.
>> When that goes over 4GB, the file cannot be stored in the filesystem the usb/iso uses.
>>
>> More details here:
>> https://forums.linuxmint.com/viewtopic.php?p=1123257&sid=5c42d363988a2c6980ae256697991aa1#p1123257
>>
>> Best,
>> Angelos
>>
>> On 12/17/20 12:28 PM, Gandalf the Gray wrote:
>>> Hi Angelos
>>>
>>> Just a quick question about the ISO size limit that has been bugging me
>>> last night.
>>>
>>> How does projects like Scientific Linux or RHEL manage to get ISOs of more
>>> than 4GB?
>>>
>>> I think that the aim of the OSGeoLive project is to fit the ISO on a DVD,
>>> am I correct?
>>>
>>> If I may be presumptuous, why doesn't the OSGeoLive project start moving
>>> away from a DVD ISO, to an iso that can run only from USB, or is this
>>> limitation of 4GB a Ubuntu issue?
>>>
>>> Please correct me if I am wrong.
>>>
>>> Pieter
>>>
>>>
>>> _______________________________________________
>>> osgeolive mailing list
>>> osgeolive at lists.osgeo.org
>>> https://lists.osgeo.org/mailman/listinfo/osgeolive
>>
>> --
>> Angelos Tzotsos, PhD
>> President
>> Open Source Geospatial Foundation
>> http://users.ntua.gr/tzotsos
>>
>>
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>>
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-- 
Angelos Tzotsos, PhD
President
Open Source Geospatial Foundation
http://users.ntua.gr/tzotsos