[lvs-users] Some users slow loading..

Graeme Fowler graeme at graemef.net
Fri Aug 3 23:59:54 BST 2007

On Fri, 2007-08-03 at 15:16 -0600, Dan Baughman wrote:
> One, physically separate load balancer. (ubuntu 6.06). Two physically
> separate real servers.  This is all brand spanking new, high end intel
> hardware.  Running DR ( with the loopback adapater on the 2k3 servers).

Aha... a thought comes to mind here.

> The real servers are using the same physical interface to respond to the
> load balanced requests as to the direct requests.


> The more hops out the more the issue presents itself.  I am trying to by
> pass the loadbalancer in the problem case to see if it is even the issue.

PMTUD, aka Path MTU discovery.

Somewhere in the path between you and your clients is a router which
isn't honouring ICMP replies telling it that DEST_UNREACH/FRAG_NEEDED.

Try tuning your MTU down on both the W2K3 servers *and* the director so
they're all 400 (you'll have to look up how to do this for your distro,
but it usually isn't hard). It'll make the network seem less efficient
on the face of it, but "less efficient" might mean "working", and if it
does then you're sorted.

If that fixes things, turn it up in increments of 100 bytes until it
breaks; that way you find the "weakest link" and can then set the MTU to
be lower than that value.


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