Re: [Xen-users] development machine with xen on gentoo

[Stephan Wentz <stephan@xxxxxxxx>]

Javier Guerra wrote:
> On Tue, Jun 3, 2008 at 2:45 PM, Stephan Wentz <stephan@xxxxxxxx> wrote:
> > Problems appear on the Dom0 when doing a lot of traffic on the harddrives,
> what happens if you use ionice to give Dom0 traffic just a little less
> priority than serving DomUs?
No that makes it even worse, iowaits stay the same and the transaction 
is even slower...
I digged a little deeper and did some tests, I found out the following. 
I stopped all DomU's and rebootet to have a clean system with only the 
Dom0 running. Then I started to scp a 20 GB image from another machine.
Speed was ok for the first 8 GB, about 50mb/s. But then suddenly the 
throughput went slowly down, to about 2-3mb/s.
What was kinda weird, the memory usage of the Dom0 increased in the 
_same amount_ of the transferred data! When 9GB where tansferred free 
showed 9,5GB used memory, after 10GB transfer it showed 10,5GB used 
memory. That rather confused me - what can this be? Is the server 
holding the copied data in memory because it can't write it fast enough?
Looking at iostat -x I saw that %utilization was always at 100% for the 
target device.
Now what's funny, when I killed scp on the remote machine the 
%utilization wasn't going down, throughput was at constant 5mb/s, for 
about 5 minutes, it seemed like he was still writing the received data 
from memory to disk.
Btw, xen version is 3.2.1.

I think that the RAID controller has to do with it (3ware 9550SX), but I 
have no clue on how to get more details to find the bottleneck.
Anyone got an idea?

Bye,
Stephan

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