Re: Deprecating NBD in favor of squashfs-over-NFS

Alkis,

I made this change to my test environment and so far it is working well.  Debian 9 with the stock LTSP.  Boot times seem to be unchanged but I do see a slight improvement in Chrome/Firefox startup.  

One question though.  We have a couple wireless bridges in production providing connectivity to a handful of wireless clients.  Performance over the bridge takes a pretty big hit so I use "LTSP_NBD_TO_RAM=true" to load the image into RAM.  This works well.  Will this option go away with NBD?  Is there an alternate way to load the image into RAM?

On a related note.  My wireless clients take about twice as long to boot using NFS over the bridge.  Once the client is booted performance is about the same.

Bob Wicksall
Computer and Network Services Manager

Pioneer Library System
2557 State Rt. 21
Canandaigua, New York  14424


----- Original Message -----
> From: "Alkis Georgopoulos" <[email protected]>
> To: "ltsp-discuss" <[email protected]>
> Sent: Friday, May 17, 2019 3:52:46 AM
> Subject: [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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