Hello,
I've been experiencing an odd problem as of late with new domUs that I've
created.
My setup:
Intel E6400 Core 2 Duo
4GB RAM
250GB LVM volume
Debian 4.0 "Etch" as dom0
Xen 3.0.3 w/PAE / 2.6.18 kernel
I've had this machine up and running since November/December (2006), and have
made a
number of paravirt
domUs. Initially by hand, and then progressing onto the Debian xen-tools
package and using
xen-create-
image. All domUs are Debian 4.0 "Etch" systems-- filesystems present as logical
volumes on
the LVM.
All has been fine and dandy (and even continues to be fine and dandy-- with
those original
domUs), until some
point when any newly created domUs created appear to have issues with
DNS/SSH/NFS. Not
sure WHY they have
problems-- but it appears I haven't been able to create a working domU using
xen-create-
image / manual
debootstrap since February/March (I'd also attribute it to the release of
Debian Etch.. but
they've all been apt-
get upgraded to the official Etch release over time). No clue why.
What happens is often first noticed by SSH attempts. The first attempt to
connect to a
troubled VM often
results in odd delays not present on the other "working" VMs, and then I get
the infamous:
"Disconnecting: Bad
packet length wxxxyyyzzz" message. Subsequent connections tend to work, only to
be
booted with a similar
"Bad packet length" message a few minutes later. NFS shares refuse to mount
from the server
(another VM on
the same machine). "rpcinfo -p nfs_server" works, but after a curiously long
delay. NFS
mounts themselves
claim "failed. NFS server is down."
Also strange, one machine seemed to be having issues pinging another VM. There
would be
delays between
icmp_seq lines, then it might go for 5-6 seemingly normal, only to act up
again. I would end
up getting about
11-25% packet loss just pinging another VM on the same machine. Installing the
host utility
and running "host
problemvm" from the problemvm yields a mix of results-- sometimes it retrieves
its DNS info
just fine.. other
times not... and still others, it'll seem to "half" find it.. returning some
malformed output.
VMs get IPs via DHCP. resolv.conf is set up properly. In fact, as far as I can
tell.. network and
general machine
configuration is identical as the working domUs. I've even dropped in copies of
config files
from working VMs,
no luck.
Now, I was suspecting possible DNS issues. I've checked... double checked..
had a couple
other people check.
Everything seems to be spelled correctly, IPs match, serial numbers
appropriately updated...
services restarted...
no malformed line endings. So I really don't know what could be the issue.
Kernel, modules, initrd are the same as the working VMs.
I've tried scouring the internet for others who may have experienced the same
problems...
nothing that seems
to come anywhere close. I did find mention on the xen-devel list to some
"nloopbacks"
parameter that had
been scaled down to 4 from 8. But if each VM is running generally only one VIF,
is that even
an issue?
Now, I will say I am running, in addition to the dom0, 8-9 domUs on one
system. I don't
know if there's some
internal limit I've unknowingly passed. I've tried booting up the "problematic"
domUs first,
then booting the
known working ones.. no change-- the working domUs still work, the newer domUs
do not.
I had it suggested that there might be an issue with the bridge interface...
but what? Is there
some kernel limit
to the number of bridges and vifs I can have?
Any strategies to try and figure this out? It is truly perplexing. No strange
errors are logged
by the dom0... I
wouldn't think it would be hardware (ie memory)... as I can create a new domU
and have it
experience the same
problems. In fact I have two such problematic domUs running right now.. and
they're both
not working as I'd
expect them to (while the other 7 working domUs are also up and running,
seemingly
working just fine).
Any suggestions would be greatly appreciated.
-Matthew
--
Matthew Haas
Visiting Instructor
Corning Community College
Computer & Information Science
http://lab46.corning-cc.edu/haas/home/
"Writing should be like breathing;
It is one of those important things we do." -- me
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