Virtual servers with different performance

Hello all,

I have a virtualmin box with lots of virtual servers on it. Mostly joomla websites. I’ve noticed for some time a very different performance for very similar websites. Accessing the slower ones with firebug, I see it stays “connecting” for a long time one the first file (the index.php). Then when it loads all other files load very quick. At the same time, other joomla sites with very similar content load really quick.

TOP does not show excessive usage
IFTOP shows bandwidth is not a problem
I have enough hard drive space.
MySQL responds quickly when querying manually

So, first question is: how do I check where is the bottleneck? Apache?

And how do I configure the system for optimal performance?
Here’s the Virtualmin Information:

Virtual servers 108
DNS domains 83
Virtual websites 88
SSL websites 2
Mail domains 59
Databases 139
Mail/FTP users 713
Mail aliases 872

Server :
8 core Intel® Xeon® CPU E5506 @ 2.13GHz
500 GB HD (200 GB free)

Thank you

  • Rogerio

So, first question is: how do I check where is the bottleneck? Apache?

Well, chances are what you’re seeing is an issue with the application… Joomla in this case. Perhaps a plugin is taking awhile to work, for example.

You could always try disabling the plugins being used on one of your slow domains, and see if it speeds up after disabling one plugin in particular.


A long initial delay and then fast responses might be an indication of name resolution problems. You might want to check if your nameservers are configured correctly or if maybe one of them times out.

Thanks guys, I’ll check for bad Joomla Plugins.

And I think name resolution can in fact be the problem. How do I check if BIND is working correctly? Log files? I could not find them.
The check configuration option on Virtualmin doesn’t report any problem.
Is there way to stress test BIND and identify problems?

I’ve done a quick google search for “online DNS server checks”, but no luck.

Thank you is a good resource for extensive DNS checks. You enter a domain name and it reports any issues that might prevent correct resolution by clients.

Thanks Locutus,

It seems I have a problem. I checked one of the slow domains, and got some errors.

How do fix that with virtualmin?

Thanks a lot.

It seems there is a discrepancy of what nameservers are responsible for your … domain, as seen by the registrar and the actual nameservers.

The registrar/NIC (the prime contact point to find out which servers to ask for name resolution of a given domain) says it is “” and “”, but when querying those two servers, they say it is “”.

Well, since “linux03” and “ns2” resolve to the same IP address, that SHOULD not be a problem, but still. Whoever operates “ns1/” should make sure that the NS entries in their zones match what the NIC thinks the nameservers are.

Normally, you’d want two actual nameservers which reside in separate /24 networks.

Thanks Locutus,

It seems all my Virtual servers have that problem. I guess it was when I had a hardware failure and restored the backups from all the servers on a new virtualmin box. I’ll move them again to a new server soon, so I’ll fix it while doing it.

So I guess DNS is not my main problem. I’ve attached a printscreen from Firebug, showing that the DNS lookup takes about 1s, and after that there’s a “waiting” of more than 10s.

Attaching the file didnt work, please check

I’m stil trying to find a plugin/component on Joomla that might be causing this.


Back to DNS again! The wait time was the database connection, that was configured as “” instead of localhost. So the DNS lookup was taking too long.

It appears that linux02.intercode, and are taking too long to resolve.
How do I fix this two records?