Re: [OSR-devel] iSCSI Root

[Marc G. <gr...@at...>]

On Friday 12 October 2007 10:03:21 Gordan Bobic wrote:
> On Fri, 12 Oct 2007, Marc Grimme wrote:
> >>>> Now, in theory, I should be able to bring up another node on the same
> >>>> file system. All I would need to do is clone the /boot partition to
> >>>> the other box, and it should just come up.
> >>>
> >>> Why cloning it and not using the same. Isn't that possible. We are
> >>> always doing it this way.
> >>
> >> Because I'm not booting this off DHCP. I'm booting the kernel and the
> >> initrd off the local disk. So I need to clone the boot partition with
> >> the kernel and the initrd to each of the nodes.
> >
> > ok.
> > How about PXE. IMHO you could use one shared bootimage couldn't you?
>
> Sure I could - but I'd still prefer to reclaim all the initrd memory. No
> point in wasting it when I have an 80GB RAID1 local disk that'll only ever
> get used for swap and /tmp.
>
> >>>> As far as unsharing things under /var, I _think_ only /var/lock
> >>>> actually needs to be unshared. Can I do this with the running image
> >>>> with:
> >>>>
> >>>> com-mkcdsl -r / -a /var/lock
> >>>
> >>> you can skip the -r/ it is default.
> >>> How about /var/run, /var/log, /var/cache, /var/tmp, /var/spool. All of
> >>> these normally need to be hostdependent.
> >>
> >> I'm not sure why /var/cache and /var/spool would need to be host
> >> dependent. I can see reasons why I'd want to them to be shared.
> >
> > I think e.g. /var/spool/mail or just from the name it should be. But it's
> > up to you.
>
> I would _definitely_ prefer to have /var/spool/mail shared. More to the
> point, I'm planning to use this cluster for a big mail system with
> maildirs, so it'd better work! :-p
>
> >> I agree that /var/run and /var/lock should be private.
> >>
> >> It would be _nice_ to have a shared /var/log, but from past experience,
> >> the logs will get messed up when multiple syslogs try to write to them.
> >> Is there a shared logging solution for this? I know I can pick a master
> >> log node and get syslog pointed at this, but this won't work for all the
> >> other non-syslog services (e.g. Apache).
> >
> > Why did I want to say (use a syslog-server)? Right with apache it does
> > not work. For e.g. apache we've written a log analysis tool to merge the
> > logs. It's in the addons channel and is called mgrep.
> > I think I also read a howto integrate apache into syslog somewhere.
>
> Or there is a Spread based Apache logging system. I know there are
> workarounds. Shame logging doesn't work as atomic writes - that would
> have made things much easier for this scenario... :-(
>
> >> I plan to link /var/tmp to /tmp, and have /tmp mounted to a big local
> >> partition (local disks are only planned to have /boot, /tmp and swap).
> >>
> >> Which brings me to the next question - how do I use a local disk
> >> partition instead of the initrd? What's the procedure for that? It seems
> >> a more efficient solution than relying on a ramdisk that eats memory
> >> after booting up when there is plenty of local disk space available. How
> >> do I use /etc/sysconfig/comoonics-chroot ?
> >
> > Yes. So I suppose you don't want to configure your local disk with lvm
> > ;-) .
>
> LOL! I'd prefer not. :-)
>
> > So I'll explain it without.
> > It's basically quite easy:
> > 1. For every node: spare one partition for the chroot (let's say it
> > is /dev/sda4) and let it be at least 500M.
> > 2. For every node: mkfs.ext3 /dev/sda4
> > 3. Add to the com_info section for every node the following:
> > <chrootenv mountpoint="/var/comoonics/chroot" fstype="ext3"
> > device="/dev/sda4" chrootdir="/var/comoonics/chroot"/>
> > 4. Make a new initrd
> > 5. reboot every node
> > That's it no everything should be running on your local disk instead of
> > tmpfs.
>
> OK - how does this work, then? Does it copy the initrd to the disk at
> boot time? Or does the mkinitrd build the init root straight on that
> partition? Or does something else happen? What does
> /etc/sysconfig/comoonics-chroot do, then? I thought it had some part to
> play in this.
So first the initrd is loaded into RAM. This we cannot change. Then the 
localdisk is setup (linuxrc.generic.sh lines 279-288).

>
> Gordan
>
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-- 
Gruss / Regards,

Marc Grimme
http://www.atix.de/               http://www.open-sharedroot.org/