[Fedora-livecd-list] persistence testing howto

[Douglas McClendon]

Mike Dickson wrote:
> I just finished trying to download JBoss Developer Studio and installing 
> it on the thumb drive.  It filled up again.  I then dropped the .jar on 
> the stick hoping that I could install from that and it filled up again.  
> Checkmate. 

What size snapshot file are you using?  I think my example used 128M, 
which was of the mindset of a 700MB livecd and a 128M persistence file 
on a 1G liveusb.

You might have better luck with a 1G persistence file on a 2G usbstick.

In general what you really want to do is install the main stuff as part 
of the spin, and only use the persistence feature for the end-users so 
they can install some smaller one-off library (or such) for their 
particular needs.

Likewise, persistence can be used to edit /etc/fstab permanently to 
mount a seperate /home partition from a different filesystem image file, 
which won't suffer some of these issues (but obviously isn't useful for 
yum installing anything).

Gotta get back to watching the bowl...  At some point I hope to write up 
a web page better describing the mechanisms here, to help people 
understand the limitations of this method, and how best to work around 
them.  This is definitely not a magic bullet solution.

more later...

-dmc


> 
> MikeD
> 
> On Thu, 2008-01-03 at 15:30 -0800, Mike Dickson wrote:
>> Ran that and yes the snapshot area filled up BEFORE the errors.  Let 
>> me know what I can do....
>>
>> MikeD
>>
>> On Thu, 2008-01-03 at 16:31 -0600, Douglas McClendon wrote:
>>> Mike Dickson wrote:
>>> > Guys,
>>> > 
>>> > I got a LiveCD + Persistence usb drive running from your scripts, but 
>>> > got I/O errors if I tried to do a yum update.
>>> > 
>>> > Before that I was able to vi test.txt and put some text in and it 
>>> > survived a reboot.
>>> > 
>>> > What can I do to address the i/o errors?
>>>
>>> My first question/explanation would be that you filled up the snapshot 
>>> device.  This is quite possible, as a yum install involves creating 
>>> several copies of the actual files you end up installing.
>>>
>>> The way to see if this is what is happening would be to have another 
>>> terminal open, and periodically watch the output of "dmsetup status". 
>>> As new blocks are written to the rootfs snapshot device, you will see 
>>> the snapshot filling up.
>>>
>>> If you get these IO errors even before the snapshot fills up, please try 
>>> to post some more detailed output.
>>>
>>> In general, as discussed there are pros and cons with this method, and a 
>>> unionfs method.  I do think there are ways to work around the cons of 
>>> this method in such a way that it is useful.  For instance, I'll play 
>>> around and see if I can prescribe a process of using yum that will get 
>>> it to create all of its intermediate files in a native tmpfs (/dev/shm 
>>> or the like) instead of the rootfs, so that they don't eat into the 
>>> snapshot space.  Likewise, now that I have my first actual tester, maybe 
>>> I'll figure out some other creative ways to improve the method (I have 
>>> some ideas I need to experiment with...).
>>>
>>> Thanks,
>>>
>>> -dmc
>>>
>>>
>>>
>>> > 
>>> > MikeD
>>> > 
>>> > "Messsage from syslogd at localhost <mailto:syslogd at localhost> at
>>> >   kernel: journal commit i/o error"
>>> > 
>>> > 
>>> > On Wed, 2008-01-02 at 04:07 -0800, Mike Dickson wrote:
>>> >> I have some time now.  I am attempting this tonight and tomorrow.  I 
>>> >> will let you know.
>>> >>
>>> >> MikeD
>>> >>
>>> > 
>>> > 
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