[node-devel] run ovirt-node in non-livecd mode

[Mike Burns]

On Wed, 2013-01-23 at 16:57 +0800, simonjin wrote:
> On 01/17/2013 08:24 PM, Mike Burns wrote:
> > On Thu, 2013-01-17 at 09:43 +0800, Wenyi Gao wrote:
> >> On 2013-01-16 19:47, Mike Burns wrote:
> >>> On Wed, 2013-01-16 at 13:33 +0800, Wenyi Gao wrote:
> >>>> Hey,
> >>>>
> >>>> Currently, the ovirt-node hypervisor runs in livecd mode, that is the
> >>>> root filesystem is read-only.
> >>>> We have to run "persist" command for persistent files, which is
> >>>> inconvenient for some uses who
> >>>> run ovirt-node only as hypervisor alone. So do we have plan to let
> >>>> ovirt-node run non-livecd mode?
> >>>> Thanks.
> >>> Hi Wenyi,
> >>>
> >>> ovirt-node doesn't just run in livecd mode, it *is* a livecd.  If you're
> >>> using ovirt-node with ovirt-engine (or derivative builds like RHEV-H
> >>> with RHEV-M), then you shouldn't have any need to persist anything
> >>> manually.  This is handled by the vdsm and ovirt-node packages
> >>> automatically.
> >>>
> >>> There is no plan to let it run in any mode other than livecd.  There are
> >>> other options in those cases, like running a full OS rather than an
> >>> ovirt-node iso.
> >>>
> >>> Thanks
> >>>
> >>> Mike
> >> Hi Mike,
> >>
> >> Thank you very much for answering the question. My case is we are using
> >> ovirt-node
> >> as hypervisor standalone without ovirt-engin or RHEV-M.
> >>
> >>
> >> So could you have some ideas to keep the rootfs writeable into disks
> >> persistently
> >> not into  tmpfs? Like overlay file system?
> > There isn't really a way unless you are building the image yourself from
> > scratch, and even then, some things won't work as you would expect them
> > to.
> >
> > One possibility:
> >
> >        * add / to the rwtab or an rwtab.d file -- this makes everything
> >          writable, though not persistent.  It needs to be done at build
> >          time, though.
> >        * when installing, install with a very large Config partition.
> >          It's 5MB by default, but you will need far more than that.
> >        * persist the directories that you want persisted.  This will
> >          automatically persist everything in those directories
> >          to /config.  You probably don't want/need /var persisted since
> >          that is generally runtime-only data.  /data /var/log and /config
> >          are already backed by real storage, so no need to persist those
> >          either.
> >
> > In general, I don't recommend this.  There may be things that just don't
> > work the way you would expect.  The method for combining the 2
> > filesystems is done through bind-mounts which happen during the boot
> > process.  Therefore, some things that get persisted don't get
> > bind-mounted early enough in the process to be used correctly.  These
> > need special handling in the ovirt-early service.
> >
> > One other thing you could try is altering /etc/fstab in the base image
> > to symbolically link some directory in /data.  /data is backed by real
> > storage, so that would theoretically work as well and might be safer.
> > The change needs to be done in the base image at build time or using
> > something like a plugin to make this change.
> >
> > Hope this helps
> >
> What if we install ISO to disk and not using the way  copying the 
> squashfs img, we copy the squashfs filesystem and mount root fs as rw,
> like the way we install a LiveCD Fedora to disk.
> Do you think it's  possible the ovirt-node would support in case some 
> custom won't use a stateless ovirt-node and not working with ovirt-engine.

It's something that could work for installation, but upgrades would be
very different, a lot of assumptions we make in our code would need to
change (assuming we need to persist, change everything that looks at
where the the livecd is mounted, etc).  It's not a simple change to make
everything work the same way in that environment.

If it's something you're really interested in, you can submit patches to
make it work that way, though.

Mike
> 
>   -Simon
> > Mike
> >
> >
> >>
> >>>> Best regards
> >>>> Wenyi Gao
> >>>>
> >>>> _______________________________________________
> >>>> node-devel mailing list
> >>>> node-devel at ovirt.org
> >>>> http://lists.ovirt.org/mailman/listinfo/node-devel
> >
> > _______________________________________________
> > node-devel mailing list
> > node-devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/node-devel
> >
> 
> 
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