> From: James Heather <email@example.com>
> To: <firstname.lastname@example.org>
> Date: 03/11/2013 09:37
> Subject: Re: [Fedora-livecd-list] "Input/output
error" and/or "Bus
> error" for most commands
> Sent by: email@example.com
> > Critical limitation
> > LiveOS overlays are employed as write-once files, which always
> > space—never releasing space for reuse. Should the overlay storage
> > space, whether temporary or persistent, be totally consumed,
> > system will likely crash with Input/output or Bus errors. If
> > crash does occur while using temporary storage space for the
> > a simple reboot will rectify the situation. With persistent
> > the situation is more dire and will require ... (I don't know
> > case at all). In either case, achieving the reboot likely
> > require a hard reset since attempting a software initiated reboot
> > probably fail with more Input/output or Bus errors.
> ... will require appending "reset_overlay" (think that's
right) to the
> kernel command line on boot-up, which will reset the state to its
> initial boot (though it won't reset a persistent home, of course).
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.
> It's not quite true that a live overlay will never release space.
> think if you created a file that got stored in the overlay, and then
> deleted it, you'd reclaim the space. But what it can't do is reclaim
> space that's used by the squashfs image: deleting things from there
> do something to mark them as deleted in the filesystem, but you won't
> able to use the space, since it wasn't ever taking up any overlay
> in the first place.
> I think the overlay operates at the sector level, but I'm not certain
I left this bit out. It's good
info, but sounds like a bit of certainty could be injected. ;-)
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.