"Load Balancing": How Busy are the servers?

Marc G. Fournier scrappy at hub.org
Sun Jan 1 10:56:18 PST 2006

For all the technology, I was kinda hoping for some 'scientific formula' 

Now, I really hate to ask, but how do you use vmstat to get a feel for how 
busy the disk subsystem is?  What are you looking for?

On Sat, 31 Dec 2005, Francisco Reyes wrote:

> Marc G. Fournier writes:
>> 1. What variables on a server should be monitored to determine how busy a 
>> server is? 
> I am a fairly new sysadmin.. who inheritted nearly 20 machines, so take my 
> comments with a gain of salt. Before that the most I ever had was 7, mostly 
> DB, FreeBSD machines :-) .. and.. Hi Marc. :)
> I think it comes down to primarily 3 factors
> * RAM
> * CPU
> * DISK
> If you are hitting Swap, you are either running too many programs/services or 
> too many users.
> Same for CPU
> Disk are different in that the same number of disks can perform different 
> based on what raid controller and what type of RAID.
> I use top and load average to determine if a machine is up to capacity in 
> memory/cpu.
> I use vmstat to determine if the disk subsystem is falling behind.
> BIG NOTE: The one thing that I have yet to really pay much attention is the 
> network performance. Fortunately we just hired someone who has significantly 
> more experience on that area. :-)
>> 2. Are there any tools that I can run to give me a point in time "summary" 
>> of how busy a server is based on these several factors?
> I think there are lots of tools. Some vary from SNMP capture/graphing, to 
> custom made tools done in-house. I think it's a combination of how difficult 
> it is to setup vs what you need to monitor. 
> At work we are just starting to roll out an SNMP tool. The new hire is 
> leading the effort so I am not very familiar with the setups.. the one thing 
> I see so far is that ultimately, there usually are things that one needs to 
> monitor that is unique to your organization and you need to either integrate 
> a program into the tool or do your own independant monitoring of that 
> particular resource.
> I think the ISP list may be a good resource since the needs of the average 
> user are different from ISPs/companies with numerous machines. 
>> Basically, I'd like to keep track of multiple servers and be able to say 
>> "this server is running >75% of capacity, time to upgrade or move things 
>> off of it" ... if its possible ... ?
> In my opinion, for the most part, the answer is yes. The problem is usually 
> how long it's going to take you to setup the environment to monitor the 
> servers.
> The program we went with was chosen because the new hire was familiar with 
> it, but a search on the archives for "monitoring tools" will give you a long 
> list of programs and opinions of which are easier.
> If I had the time, I think I would likely write my own tool. This way I will 
> be able to measure exactly what I want. Right now I thik we will cover most 
> basics with the tool we are going with, but will need to still do our own 
> custom apps to monitor a number of resources and metrics.

Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy at hub.org           Yahoo!: yscrappy              ICQ: 7615664

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