Fwd: [Ltsp-discuss] Deprecating NBD in favor of squashfs-over-NFS

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Fwd: [Ltsp-discuss] Deprecating NBD in favor of squashfs-over-NFS

Dominik George-7
Hi,

I will be testing this in some Debian Edu setups and report.

Meanwhile, what do others think?

-nik


-------- Original Melding --------
Fra: Alkis Georgopoulos <[hidden email]>
Sendt: 17. mai 2019 09:52:46 CEST
Til: [hidden email]
Emne: [Ltsp-discuss] Deprecating NBD in favor of squashfs-over-NFS

NBD is used for the LTSP client root file system, /.
SSHFS is used for /home and is unrelated to this discussion.

NBD has some issues; instability; no reconnections; can't survive server
reboots; difficult configuration; etc.

In the past, NBD replaced NFS in LTSP because the squashfs image has
less metadata and is compressed, so it's a lot faster than an
uncompressed directory.

The best of both worlds is to export the squashfs image over NFS.
So, the server will export /opt/ltsp/images via NFS,
and the clients will connect to /opt/ltsp/images/amd64.img,
and "loop-mount" it as their root file system.
To be clear: you'll still need to run `ltsp-update-image` like before.

LTSP5 already supports this; we just haven't tried it in production a
lot. For the new LTSP, we'll probably default to that and stop using NBD
completely, unless you report issues.

So, if anyone wants to switch NBD to NFS now, aiming for better
performance and stability, he'd need to do these:

sudo apt install --yes nfs-kernel-server
sudo ltsp-config nfs
sudo gedit /var/lib/tftpboot/ltsp/amd64/pxelinux.cfg/default

and in that file, replace lines 13-14 from something like this:
kernel vmlinuz-4.15.0-45-generic
append ro initrd=initrd.img-4.15.0-45-generic init=/sbin/init-ltsp
forcepae root=/dev/nbd0

to something like this:
kernel vmlinuz-generic
append ro initrd=initrd.img-generic init=/sbin/init-ltsp forcepae
root=/dev/nfs nfsroot=/opt/ltsp/images ltsploop=amd64.img

The change will be overwritten the next time you run ltsp-update-image;
so if you're happy with the change and you want to make it stick,
the "default" file there is a symlink to "ltsp";
remove the default symlink and run `cp ltsp default`.

(longer explanation: ltsp-update-kernels creates symlinks for the latest
kernel, so "vmlinuz-generic" is a symlink to the latest kernel,
and it only updates the pxelinux.cfg/ltsp file, not the "default",
so this allows us to maintain pxelinux.cfg/default manually without LTSP
overwriting it)

Btw, status update for the next LTSP: it's being developed in a rapid
pace and will see its first release in September, so it will be called
ltsp 19.09.

Cheers,
Alkis


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Re: Fwd: [Ltsp-discuss] Deprecating NBD in favor of squashfs-over-NFS

Wolfgang Schweer-3
Hi Dominik,

On Fri, May 17, 2019 at 10:12:51AM +0200, Dominik George wrote:
> I will be testing this in some Debian Edu setups and report.

Very good.
 
> Meanwhile, what do others think?

I can confirm that it works in my virtual test environment without any
problems, but that doesn't tell much. Tests in real world deployment
would be nice.

Wolfgang

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