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[Xen-users] Crash: domU NFS server hosting domU filesystems


  • To: <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: "Samuel Torton" <samuel@xxxxxxxxxx>
  • Date: Fri, 24 Feb 2006 13:37:13 +0100
  • Delivery-date: Fri, 24 Feb 2006 12:37:52 +0000
  • Importance: Normal
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Hi,

We have two physical machines "host1" and "host2", IBM Bi-pro Xeon 3.0 Ghz +
RAM 3 GB, each running Xen 3.0.1, and hosting domU machines.

- dom0: "host1": RAM 512 MB + LVM filesystem
- dom0: "host2": RAM 512 MB + NFS client


-1- First config and performed tests:
-------------------------------------

--> "host1" dom0 machine hosts a domU machine "guest1"
    . "guest1" is a NFS server
--> "host2" has a mount on "guest1" NFS server

|---------------------------|     |---------------------------|
| dom0: "host2"             |     | dom0: "host1"             |
|       RAM: 512MB          |     |       RAM: 512MB          |
|                           |     |                           |
|       NFS client          |     |       LVM                 |
|       + mount on "guest1" |     |                           |
|       /nfs/guest1/data    |     |                           |
|---------------------------|     |---------------------------|
           |                                    |
           |                      |---------------------------|
           |                      | domU: guest1              |
           |                      |       RAM: 512MB          |
           |                      |                           |
           |----------------------|-----> NFS server          |
                                  |       /data               |
                                  |                           |
                                  |---------------------------|

Tests from "host2":
create files in /nfs/guest1/data folder, with "dd" command.
example: --> dd if=/dev/zero of=/nfs/guest1/data/x.fs bs=1024k count=xxxxx
I am able to create very huge files (up to 10 GB and more...), and all the
machines (dom0 and domU) behave correctly, without crashing.
With this kind of tests, I can say I'm confident with NFS server and client
config.

Now, I will do the following tests...


-2- Second config and performed tests:
--------------------------------------

I have exactly the same config as step -1-, but I'm adding a new domU
machine named "guest2".

--> "guest1" NFS server stores the domU "guest2" filesystems
    (root.fs, data.fs, var.fs, swap.fs, etc...)
--> "host2" dom0 machine runs the domU machine "guest2"
    the Xen guest2.cfg looks like this:
      ...
      disk =  ['file:/nfs/guest1/data/guest2/root.sfs,sda1,w',
               'file:/nfs/guest1/data/guest2/swap.sfs,sda2,w',
               'file:/nfs/guest1/data/guest2/tmp.sfs,sda3,w',
               'file:/nfs/guest1/data/guest2/var.sfs,sda4,w',
               'file:/nfs/guest1/data/guest2/data.sfs,sda5,w']
      ...

|---------------------------|     |---------------------------|
| dom0: "host2"             |     | dom0: "host1"             |
|       RAM: 512MB          |     |       RAM: 512MB          |
|                           |     |                           |
|       NFS client          |     |       LVM                 |
|       + mount on "guest1" |     |                           |
|       /nfs/guest1/data    |     |                           |
|---------------------------|     |---------------------------|
           |                                    |
|---------------------------|     |---------------------------|
| domU: "guest2"            |     | domU: "guest1"            |
|       RAM: 512MB          |     |       RAM: 512MB          |
|                           |     |                           |
|                           |     |       NFS server          |
|                           |-----|----->/data/guest2/*.fs    |
|                           |     |                           |
|---------------------------|     |---------------------------|

Tests from "guest2":
create files in /data folder, with "dd" command.
example: --> dd if=/dev/zero of=/data/x.fs bs=1024k count=xxxxx
I am able to create files, but if i try to create files bigger than 100 or
200 MB, I get a very big crash on domU "guest2" machine, and even on dom0
"host2" machine !!! It's not really a crash, but both machines totally
freeze.

"host1" and "guest1" are not impacted at all,
but I can't do anything on "host2" and "guest2... except rebooting manually
the physical machine !!


I'm pretty convinced it's a Xen bug, but I would like to have confirmation
from Xen team ?
Do you think this issue will be solved in Xen 3.0.2 release ?

Here are some other hints:
- If I increase RAM size on "host2", the crash still happens;
- If I swapoff "host2" and "guest2", the crash still happens;
- I thought to have found a workaround to avoid the crash, but it still
crashes:
  in the "guest2" /etc/fstab file, I set ALL disk options to "sync"
  --> performances are totally degraded, and still crashes with bigger files
!


Thank you for your help,

Samuel




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