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Old 03-31-2010, 02:09 AM
Steve Rippl
 
Default recommend a disk setup for LTSP install?

john wrote:
> Hi all,
>
> I have come to the conclusion that my single 7k sata disk is too slow to serve
> 25 plus LTSP thin clients. I see high disk writes accompanied by high
> CPU wait time.
>
> My mobo supports SAS. I am wondering what the optimal disk setup is
> with regard to speed. Can I get
> away with a single 10-15K SAS drive or should I be looking to setup
> raid 5, 6, or 10? How about
> two disks, a sata for the OS and a fast SAS for /home/ /tmp ?
>
> I'd appreciate some advice!
>
> Thanks!
>
> John
>
>
I guess it depends on what you need in terms of redundancy versus
maximizing available disk space versus speed! For max speed (and no
redundancy) use a pair of stripped (RAID 0) sas drives. Use 2 such
pairs (one for the os, one for /home) for even better performance...

On our LTSP servers we use 2 pairs of RAID 1 sata drives (might be 10k
rather then 7k), one pair for os, one for /home folders. That works
well enough, redundancy and some speed gains (faster reads, slightly
faster write) and no load due to IO wait that I've seen.

You don't want RAID 5 or 6 if you want speed.

We only use sas drives on our virtual server hosts (along with RAID 10)
where we're really looking for high speed raid arrays.

The bottom line is I don't think you need to pay for sas for LTSP, you
can buy 2 sata drives for less than one sas, mirror them, get redundancy
and plenty of performance (or strip them if you don't care about
redundancy to get even more speed, but wouldn't you want your server to
keep working if one drive failed?)

Steve


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Steve Rippl
Technology Director
Woodland Public Schools
360 225 9451 x326


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Old 03-31-2010, 04:11 PM
Nicolas Roussi
 
Default recommend a disk setup for LTSP install?

John,
I would recommend a single cheap SATA drive for the OS and a RAID 5 for /home. I am running 2 servers that serve 30-35 clients each. On each server I have a Seagate 750GB 7.2k for the OS. When the drive craps out and it has in the past, I just reinstall the OS and I am ready to go. As for the /home, I have been trying to get the teachers and students to trust this OS that they have not used before in their life and therefore I needed redundancy for their data. A 15-disc MD1000 raid array did the trick that is shared over NFS between the 2 servers. I had data discs die in the past and the MD1000 rebuilt the array in about 4 hours. Think about the cost also; 4 SAS 300GB for RAID 5 @$330 ea is ~$1300 and another 2 SAS for the OS in RAID 0 or 1 another $600. Total of ~$2000 just for drives. If you go the SATA option, it's just $50 a pop.

Take a look here as well: http://www.acnc.com/04_00.html a nice visual representation on RAID levels

Regards




Hi all,



I have come to the conclusion that my single 7k sata disk is too slow to serve

25 plus LTSP thin clients. I see high disk writes accompanied by high

CPU wait time.



My mobo supports SAS. I am wondering what the optimal disk setup is

with regard to speed. Can I get

away with a single 10-15K SAS drive or should I be looking to setup

raid 5, 6, or 10? How about

two disks, a sata for the OS and a fast SAS for /home/ /tmp ?



I'd appreciate some advice!



Thanks!



John







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Old 04-01-2010, 01:39 AM
john
 
Default recommend a disk setup for LTSP install?

Thanks to all for these replies. It'll take me a couple of days to digest them.

One thing I'll throw out there it my impression that server sizing is
not an easy thing to figure out. Several of the links that used to
appear on the ltsp.org wiki are broken, and the edubuntu/LTSP manual
that has various online incarnations tends to undersell the
horse-power needed for the server IMO.

Even after 3-4 years of running LTSP installations I can't figure out
just how many active users/TC's I should be able to hang off a Quad
Core 3 Ghz opteron with 16 Gigs ram. I've seen figures between 20-150.
My experience show's about 20-25 before performance goes to the dogs.
I've been told that local apps changes the equation, but I am waiting
for the next Ubuntu LTS before I iterate.

Oh, heck, I'll throw out another thing :-)

I was surprised to see that there was so much disk write activity. I
am trying to figure out what is getting written where. I found a tool
called IOTOP that should correlate disk i/o to particular apps.
Unfortunately it uses some kernel hooks that aren't supported by
Ubuntu kernels so i am in the process of compiling an ubuntu kernel
with the proper stuff included.

Does anyone know where all the disk writes might be coming from and
going to? Is there a lot of writing to users mozilla profiles or /tmp?

Thanks!

John

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