<tt><font size=2>> From: James Heather <j.heather@surrey.ac.uk></font></tt>
<br><tt><font size=2>> To: <livecd@lists.fedoraproject.org></font></tt>
<br><tt><font size=2>> Date: 03/11/2013 09:37</font></tt>
<br><tt><font size=2>> Subject: Re: [Fedora-livecd-list] "Input/output
error" and/or "Bus <br>
> error" for most commands</font></tt>
<br><tt><font size=2>> Sent by: livecd-bounces@lists.fedoraproject.org</font></tt>
<br><tt><font size=2>> <br>
> > Critical limitation<br>
> > LiveOS overlays are employed as write-once files, which always
consume<br>
> > space—never releasing space for reuse. Should the overlay storage<br>
> > space, whether temporary or persistent, be totally consumed,
the<br>
> > system will likely crash with Input/output or Bus errors. If
such a<br>
> > crash does occur while using temporary storage space for the
overlay,<br>
> > a simple reboot will rectify the situation. With persistent
storage<br>
> > the situation is more dire and will require ... (I don't know
this<br>
> > case at all). In either case, achieving the reboot likely
will<br>
> > require a hard reset since attempting a software initiated reboot
will<br>
> > probably fail with more Input/output or Bus errors. <br>
> <br>
> ... will require appending "reset_overlay" (think that's
right) to the<br>
> kernel command line on boot-up, which will reset the state to its<br>
> initial boot (though it won't reset a persistent home, of course).</font></tt>
<br>
<br>
<br><tt><font size=2>I've updated the page with this much and confirmed/noted
that "reset_overlay" is the former (but now deprecated) form
of "rd.live.overlay.reset". Please review/adjust as necessary.</font></tt>
<br><tt><font size=2><br>
<br>
> It's not quite true that a live overlay will never release space.
I<br>
> think if you created a file that got stored in the overlay, and then
you<br>
> deleted it, you'd reclaim the space. But what it can't do is reclaim<br>
> space that's used by the squashfs image: deleting things from there
will<br>
> do something to mark them as deleted in the filesystem, but you won't
be<br>
> able to use the space, since it wasn't ever taking up any overlay
space<br>
> in the first place.<br>
> <br>
> I think the overlay operates at the sector level, but I'm not certain
of<br>
> that.<br>
> <br>
> James<br>
</font></tt>
<br><font size=2 face="sans-serif">I left this bit out. It's good
info, but sounds like a bit of certainty could be injected. ;-)</font>
<br>
<br><font size=2 face="sans-serif">Also along these lines, a coworker was
playing with the 'discard' mount option to see if the kernel's TRIM support
would help here. Testing showed that it does not and further research
discovered kernel mailing list comments stating clearly that this feature
is not yet available for the COW images.</font>
<br><font size=2 face="sans-serif"><br>
--<br>
John Florian</font>
<br>