USB Live Ubuntu Persistence

[Joseph Sinclair]

Eric Shubert wrote:
> Eric Shubert wrote:
>> Dazed_75 wrote:
>>> Saturday I was helping Matthew create a Live Ubuntu USB stick.  We 
>>> succeeded but for some reason persistence was not working and I could 
>>> not figure out why.  I did the same thing here at home and persistence 
>>> works fine.  In fact, I think I know the answer now.  Mathew was using a 
>>> 16 GB flash drive and wanted the rest of the drive used for persistent 
>>> storage. 
>>>
>>> The problem was, I believe, that the flash drive was formatted for FAT32 
>>> which has a file size limit of 4GB.  It appears the utility to create 
>>> the LiveUSB ubuntu stick creates a special file to use for the "overlay" 
>>> (my term) file system that is merged onto the read only filesystem from 
>>> the Live image.  Since we were asking it to make a 14.4GB overlay file 
>>> on a FAT32 partition, that part of the install failed silently and 
>>> persistence was was working.
>>>
>>> Mathew, I believe there are several ways to resolve this with the 
>>> simplest being to only ask for 4GB of persistent storage.  The rest of 
>>> the stick should still be usable though you may find it handy to make 
>>> the rest a separate partition and mount it within the LiveUSB Ubuntu.  
>>> You should even be able to make the mount persistent.
>>>
>>> -- 
>>> Dazed_75 a.k.a. Larry
>>>
>> That sounds like a possibility all right. TTBOMK though, FAT32 has a 2G 
>> file size limit. :(
>>
> 
> Now that I think of it though, are we confusing partition vs file sizes? 
> The 'overlay' partition would be what's over 2G, not a file. From what 
> I've seen of overlay filesystems, there are still going to be 
> independent files within the partition. It's not just one big file. As 
> such, I doubt this is the problem. As always, I could be wrong. I think 
> I was on that last post (except for the 2G part!).
> 
Most mixed live/persistent distros use a single file loopback mounted as the overlay filesystem (via overlayfs or unionfs), including IIRC Ubuntu live/USB.  As such, the entire persistent partition is, indeed, limited to the *file* size limit of the host partition.
Most virtual machine systems have similar problems (which is one more reason why it's good to *not* put virtual disk files on systems using FAT or NTFS, poor windows users...).