Xen users - Feb 2011 - Some observations on live migration & solution solicitation

Hello,

I am now testing XEN live migration on 3 physical hosts with XEN 4.0.1 pvops
Ubuntu 10.10 (2.6.35-22). The kernel is compiled and built with default
selections plus the support for ext4 file system as well as the support for
network file system server. The three hosts are connected by one D-link
gigabit switch (DGS-2205).

I find that:

1) If the 3 hosts are booted about the same time, the live migration is
working. (Working in this sense means that the downtime is within 1 minute.)
However, between any of the two hosts, the downtime is asymmetric. In one
direction, the downtime is constantly short, measured by loss of 0-1 packets
via ping command to the migrated guest domU. But, in the other direction,
the downtime is long and unstable, measured by loss of 40-50 packets on
average via ping command to the migrated guest domU. However, in some cases,
which are not so often observed, the downtime can be as short as loss of 3-6
packets.

2) If one host is rebooted later, then live migration to the rebooted host
will not work. The migrated guest domU on the rebooted host will not respond
to the keyboard through ssh connection.

3) I also tried regular migration. It seems that  the downtime gap between
the regular migration and the live migration is marginal. I am wondering if
there is some special requirements (kernel, hardware, etc.) for enabling
live migrations?


My expectation (for proceeding to the next step) is to have low downtime
between two hosts (loss of 0-1 packets) in both directions, and I understand
that there should be some configurations required. So could anyone tell what
my current problem might be? (I am new to this area, please forgive about my
simple questions if any.)


-- 
Cheers,

Wenda Ni, Ph.D.
Dept. of Computer Science and Engineering
State University of New York (SUNY) at Buffalo


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