Joseph Sinclair wrote:
> 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...).
>
Thanks for chiming in on this, Joseph. I'm not terribly familiar with
unionfs/aufs, just enough to be dangerous. ;)
Can you say then, whether this single-file aspect is true for all
union/aufs implementations, or is it only because of the way it's used
by persistent distros? TIA.
--
-Eric 'shubes'
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