[GRLUG] Apologies for not making it.

[Michael Mol]

On Tue, Nov 24, 2009 at 8:17 AM, Ben Rousch <brousch at gmail.com> wrote:
> On Tue, Nov 24, 2009 at 1:25 AM, Michael Mol <mikemol at gmail.com> wrote:
>>
>> I suspect he didn't need two 32GB SSDs in RAID 0, but I don't have
>> enough context. My gut tells me GigE+netboot would work if the RAM
>> were bumped up to 16GB. File caches are wonderful things, and a full
>> install+favored apps of a desktop edition of Ubuntu 8.10 with only
>> /home put off to another drive left me with less than 7GB on /.  Heck,
>> you could conceivably make that 7GB part of an initrd. :P
>
> We did discuss some of this last night. I'm sure Darrin will correct me if
> I'm wrong, but they originally had all of the homes remotely mounted on a
> server. However with all 28 stations logging in at the same time (as a class
> starts), then the kids all using Firefox or Chromium (think cache files),

Those cache files should be staying in the in-memory file cache, or
possibly set in tmpfs.  If they're not staying in the in-memory file
cache, then something is demanding enough of the cache to push them
out. (Ergo, more memory becomes helpful.)

Putting Mozilla's profile directory in a tmpfs mount explicitly makes
the file cache the data store, but doing it that way requires a copy
step from a persistent source.

You could also potentialy disable the browser cache entirely if you
set up Squid as a caching proxy.

> the network or server drives had trouble keeping up. By moving the homes to
> local storage, they were able to take a big burden off the server and
> network.

I can understand that. Still, RAID0 of SSDs, while sickeningly fast,
seems like an expensive solution. 32GB is more than enough for
everything but /home, SSDs still aren't exactly cheap, and RAID0
severely reduces the fault tolerance.

Did each kid have his own persistent $HOME? For most of the time while
I was a student at GRCC, the students' profiles weren't persistent,
and weren't roaming. We had a mapped drive where we saved all our
files. They tried enabling roaming profiles once. First the servers
slowed to a crawl, then the servers ran out of disk space...

If the kids' $HOMEs don't need to be persistent, consider mapping a
read-only skeleton $HOME, then combining it with a tmpfs mount via
unionfs. Any local changes stay in either RAM or swap, and they go
away on logout.  Mapping, e.g. $HOME/Desktop or $HOME/Keep to a
student-specific data store lets the student keep the data they find
important. (Actually, I think the FreeDesktop project has a list of
directories which should be considered "special" in the sense that
compliant applications should keep user data organized in there, and
it may be worthwhile finding and looking at that list.)

> Still, all of the students' data (Documents, Videos, Photos, etc)
> are mapped to the server, and they are working on getting things like Gnome
> settings up there too.
>
> 8GB seems like plenty of RAM. I don't remember seeing it go over 2GB while
> four of us played with the same station.

Under my normal browse load, Firefox will often raise to around 700MB
resident.  On my x64 server/desktop box (Phenom x4 9650 with 8GB of
RAM), actual RAM usage rarely rises past 2GB, with the rest eventually
occupied by the file cache.

I've actually been thinking a lot about file caches lately.  I should
go back and tag several of my blog posts so that the LUG planet picks
them up.

...Anyway, this is the kind of discussion I was hoping for. Good
stuff, fun stuff. :D

-- 
:wq