LTSP over wireless?

Sun Jan 9 23:41:06 UTC 2011

Hi All,
Here's an update on this topic from the discussion on the edubuntu channel
today.  I edited it a bit for brevity and focus and ease of reading.  This
will be useful to document the ideas given.
David

alkisg: LTSP over wireless will be kinda slow, maybe *nx would fare better

dgroos: Possible, though?  How about with gigabit wireless with a ratio of 1
router to 10 clients?

alkisg: Sure, it's possible, as long as you have an appropriate initramfs
locally, e.g. in a usb stick
To check if the performance suffices, you can temporarily test with XDMCP,
it has the same performance as ltsp
I.e. enable xdmcp in /etc/gdm/custom.conf, and run X -query on e.g. 10
standalone clients over wireless
I've never seen a gigabit wireless link so I don't know how that would
perform

vmlintu:  fat clients might perform better over wireless

dgroos:  Right, wireless N is rated at 300 MB/sec...
Thanks for the ideas to try the XDMCP, I'll give that a go in the coming
month or 2 and get back to the list.
thanks for the idea--I would just need an additional 512 MB ram for each
thin client I'm on and they should work fine (Pentinum 4's).

vmlintu:  I should do some testing with fat clients over wireless some day
too

alkisg:  Some form of local image cloning + syncing is needed there,
otherwise with regular 50mbps wireless they're slow
I read a paper once about a modified nfs client that used lots of local
caching, that would be ideal but I don't think they're maintaining it after
the initial implementatino

mhall119:  IIRC, samba does a good job of local caching

alkisg:  mhall119: that persists across reboots?

mhall119:  probably not, no

alkisg:  That wouldn't help then :(

dgroos:  when you say 'local image cloning + syncing' do you mean that the
disk image would be stored on the USB flash drive, and that that image would
be synched during each session?

alkisg: yes, but ideally it wouldn't need to be synced as a whole, but only
the parts that the clients needs to read each time
So it wouldn't add any boot or other overhead
E.g. the user would say "reserve 1 Gb on that usb stick for caching", and
that'd be all, even if the fat client image was 10 Gb.

dgroos:  So, this is LTSP with a fat client but 'X' is stored locally on a
USB stick, with the parts of X updated as needed.  Not quite sure what this,
"X" is, yet.  Are you saying that the USB stick would have 10 GB on it or 1
GB?

alkisg:  1
dgroos:  ... So, the incrementally updated image might be about 1 gig only.
This 'cached' info, that's on RAM?  Thus the need for more than 2 GB RAM?
Or that could be on the USB stick?

alkisg:  No no it's not related to RAM, I just tried to give a similar
example
 The clients wouldn't need any additional RAM for that, the cache would be
on the usb stick, stored asynchronously so that it wouldn't add any overhead
 E.g. when you have an 1 Gb image, and a client boots, it might read just
20-50 Mb
It would store those on the stick, so the next time it booted it would just
have to ask the server "has this part changed? no? then I'll read it from
the stick, don't send it to me over the network"

dgroos:  Right.  And stick access is pretty quick!
How much work/time do you see setting up something like this would take
someone in-the-know?

alkisg:  And scales well. And local disks could also be used (e.g. ntfs
partitions), if available
 A lot, implementing properly a caching file system over the network is no
easy task. E.g. that caching nfs-client was implemented but abandoned, I'm
sure there's a reason behind it abandonment :D

dgroos:  I wonder how important this feature would be to other educators?

alkisg:  A lot, it'd be useful for 100mbps networks too, and if implemented
properly (with caching ldap) it would even allow a classroom to be still
used when a server goes down
(not exactly ltsp anymore...)

dgroos:  It seems there would be *lots* of overlap, however.

alkisg:  I think in Spain they chose to sync the image from the server on
each boot instead of using ltsp, I imagine if such a thing was implemented
they would use it too (thousands of installations there)

dgroos:  There site is powered by plone...
http://www.guadalinex.org/que-es-guadalinex

vmlintu:  Maybe the ltsp image could be sync'ed in initramfs to local hard
drive
That might be worth a try.. it'd take quite a long time to transfer a 10 gig
fat client image, though..

dgroos:  How often would this have to happen?

vmlintu:  every time the image changes, I guess
Using rsync would probably shorten the time quite a bit, though

dgroos:  could it be only the part that had changed--incremental I'm trying
to say, somehow?

vmlintu:  rsync transfers only the parts that have changed - we use that now
to transfer ltsp images to our servers

dgroos:  OK.  Could one use USB sticks instead of HD to increase speed,
significantly?

vmlintu:  most usb sticks I have tried have been slower than hard drives

alkisg:  dgroos: are you mainly talking about thin or fat clients?

alkisg:  Because if you have enough bandwidth for thin clients (sending
videos, X traffic etc) it would more than cover the networked-disk part...
not much need for caching there

dgroos:  Well, I'm very big into recycling older Pentium 3 and 4 machines so
I would say for the near future thin clients using lots of localapps, but if
it were just pentium 4's with a gig of RAM I'd say fat clients for sure.

alkisg:  dgroos: nice, but as in the local ministry proposal, I'd prefer a
little larger tables, with an ltsp server on the bottom of each table ;)
This way the netbooks/pcs/tablets/whatever there could have wired
connections to the ltsp server, and the server be wirelessly connected to
the internet

dgroos:  Excellent idea with the local ltsp server!
 I could make that work, maybe...
Would a pentium 4 with 1 gig ram be enough for a 3-computer ltsp server?
Would sch-scripts still work on them?
would it need a gig NIC?

alkisg:  That server could have 3x100mbps network cards, I think that'd be
cheaper than gigabit+switch+whatever
 sch-scripts would work, sure
About the pentium 4 with 1 gb ram... well it would work, but I don't know if
you'd be satisfied with the performance

dgroos:  How about the performance if the other 3 were running as fat
clients?  as localapps? if the server had 2 gigs ram?  I know you don't know
from experience--just asking your best guess.

alkisg:  For fat clients, you can have a very old ltsp server with just 512
MB RAM and a fast disk
No cpu/much ram is needed there
Of course if you have 2 Gb, it'll be used for caching...

dgroos:  regular 7200 fast *enough*?

alkisg:  Sure

dgroos
:  I'll be doing tests on this in the next couple of months and report back
:)
dgroos: I'll post related parts of this to my question on the list serve as
well.

alkisg:  dgroos: have you ever checked multiseat?
It allows a single pc to have lots of screens + mice + keyboards
Check the video there:
http://www2.userful.com/products/userful-multiseat-linux
There are multiple implementations, I just gave the link for the nice video

dgroos: Thanks!  I'll be checking that out as well, and adding some notes to
my blog...
[4:58PM] dgroos: Thanks alkisg, vmlintu and mhall119!
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