RE: [Xen-users] Re: Xen, LVM, DRBD, Linux-HA

["Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>]

Steve Wray wrote:
> Ross S. W. Walker wrote:
> > Please do not hijack threads, please put all your drbd questions
> > to the drbd-user list.
> 
> This is a xen issue.

Are you positive that the same symptoms wouldn't happen if
you were running a highly loaded postgres, or oracle system
on top of these drbd devices?

> I'm pretty sure its not a problem with drbd itself but with drbd under 
> xen and probably with a clash between xen networking and disk IO.

Or maybe you are reaching the capacity of your hardware?

> For people who are trying to use drbd under xen this is an 
> important issue.

It is probably an important issue for drbd users who are
running other applications too, so it wouldn't hurt to post
it to the drbd-users list as well.

> > If properly setup and maintained drbd should work properly.
> 
> I've been checking and many of our xen servers are showing similar 
> packet loss under disk IO load. However, so far, only drbd shows such 
> catastrophic problems.
> 
> Please advise as to how to configure such that disk IO does not kill the 
> network, as this *seems* to be what is happening here.

Take a 'vmstat' sampling during these periods of packet loss.

If the # of interrupts are too high then it's time to think
about, 1) interrupt throttling, 2) jumbo frames or 3) better
server.

The 'too high' mark will depend on the class cpu, bus, memory
you are running. There are ratings on the manufacturers web
sites.

-Ross

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