[K12OSN] New Building's LTSP Server

[Jeff Siddall]

On 04/18/2011 12:29 PM, Joseph Bishay wrote:
> Hello,
> 
> On Mon, Apr 18, 2011 at 9:30 AM, Jeff Siddall <news at siddall.name> wrote:
>> Personal opinions:
>>
>> You are definitely going to need more than 2 GB RAM.  CPU seems less
>> important.  I am running a quad core Phenom II, 8 GB with about 20
>> clients total, 10 or so being steadily used.
> 
> Is there a link to your specific type of machine so I can learn more
> about pricing / specs?

Nope, I build all my machines from scratch.  If you are looking at using
desktop PC parts (ie: <$2,000 systems) it is the best way to optimize
performance.  You get exactly what you want, nothing you don't.

Have a look at some parts like these as a starting point:

6 core 3.2 GHz CPU: about $200:
http://www.shoprbc.com/ca/shop/product_details.php?pid=63169

16 GB DDR3: about $225:
http://www.shoprbc.com/ca/shop/product_details.php?pid=68257

50 GB RevoDrive: about $205 each:
http://www.shoprbc.com/ca/shop/product_details.php?pid=65758

Add a motherboard of your choosing and case/PS for another $200 and you
have a pretty quick server for less than $1000.  If you need bulk
storage throw in a 2TB drive but if possible keep root and home dirs on
the SSD.

>>  No performance issues
>> except it is easy for the GigE to get saturated if there are clients
>> playing video.  Video is killer for LTSP.  If you don't install flash
>> your life will be better :)
> 
> Unfortunately as this is an elementary school, as much as I'd love to
> not have flash, I know it will be 100% required :)

Yeah, maybe look at adding an extra NIC and splitting your clients or
doing a MLT.  Someone else posted detailed instructions on splitting the
clients.

>> I would avoid SCSI drives.  Not because they are bad, but because your
>> money could probably be better spent elsewhere.  Modern SATA drives
>> perform great.  Also, definitely go with RAID1.  Not only will it buy
>> you survivability but you get 2X the read performance.  Software raid
>> works fine.  Avoid RAID5.  If you can afford it try SSDs.  They will
>> vastly increase the random IO ability of your system which is especially
>> important for LTSP.
> 
> Would you say that the much higher cost of SSD  and their read/write
> lifespan limits are still better than SCSI?

The lifespan will probably be less for a SSD but they have been making
those for a lot of years now so I don't think you will have problems in
the short term.

As for performance, the RevoDrive I referenced above will blow the doors
off _any_ platter drive at _any_ price -- SCSI or otherwise.

Even if you want to stick with platter drives SATA still performs well.
 I did an rsync to my RAID1 array of relatively slow WD RE2 GP drives
and was getting sustained _write_ speeds of well over 200 MB/s.  Not too
shabby.

Either way, the killer for platters is random IO and a SCSI drive can't
get the heads to a chunk of data any quicker than a SATA drive with the
same speed/platter configuration.

> I've been running RAID1 so I'd continue to do that for sure.
> 
>> You might be better off building two
>> smaller servers for the same price.  You might also run into scaling
>> issues with file handles and whatnot with a large number of logged-in
>> clients.  Google for people who ran into that and the resolution they
>> found.
> 
> I have been thinking about this but this would be entirely new for me
> so I'm a bit hesitant.  I also need to be able to sync the /home
> directories of a small sub-set of users when they log out with another
> remote server so I'm not sure if one location has a all-in-one LTSP
> server and the other has a different multi-server configuration if it
> will easily work or not.

If you have to sacrifice things like SSD and RAM to get to two servers
there probably isn't much benefit -- especially if you keep bandwidth
intensive stuff like flash on the clients.

>> Localapps for pig apps like Firefox may help save your server performance.
> 
> This may be the cleanest solution as 90% of the time people will be
> running Firefox.

Definitely do that if you can.  Everyone will be happier.

Jeff