Xen on CentOS - Automating Installation-Administration

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This document assumes an functioning quattor environment and an installationserver with dhcp, tftp, and pxeboot.

Needed Tools

Quattor related notes

filesystem dom0

Quattor templates: /cfg/sites/ndpf/site/filesystems/*.tpl

!!!  IMPORTANT:  !!!
*  foresee a logvol with mount point /var/lib/xen/save which will take "Speicherabbilder" of running
  domUs, when the dom0 gets the reboot command, therefore it should be 
  as large as available RAM + something (summ of all swap of domUs ?, see below)
* give each domU not more than 512MB swap, if a domU excessively uses swap it will anyways got stuck.

Naming convention:

since the Filesystem layout depends on the hardware [how many hard disks 2-4, which raid (1 or 1-0)] and on the function in terms of xen-Dom0, xen-DomU, generic, ... I used the following scheme <hardware>-<function>.tpl The filesystem Template for our Dell-Power-Edge-1950 -function xen-Dom0 would then be: pe1950-x0.tpl

Virtualization considerations

dom0 Filesystem layout

  • Dom0 (Host) needs < 10G for its system, tmp is not extensively used nor is var. To prevent the system to be unresponsive due to full / fs we could give 4GB /tmp and /var each and an extra volume for /var/lib/xen/save (size .gt. pys. RAM in dom0) to take the files in which the state of the domUs are saved (roughly comparable to hybernate a running computer). These values can be smaller if we have hardware which has some disk space restrictions.

  • For performance its best to limit the Memory of the dom0 to 512 MB and to prevent it from ballooning (i.e. takes all available memory)
  • Dom0-swap should never happen, there are no processes that consume memory, if it swaps something went wrong, just in case we can try 1 GB swap

PE-1950 configuration

Hard disks: 2 X 500GB principle layout:

  • Raid-1
  • Primary Partitions

/boot 512MB /swap 4096MB

  • LVM

Volumegroup System, Size: rest of available space I System-Volumes-Dom0 [/, /tmp, /var /var/lib/xen/save] fs: ext3 II DomU-lvms added when needed

PE-2950 configuration

Hard disks: 4 X 500GB principle layout:hardware raid-10

  • Primary Partitions

/boot 512MB /swap 4096MB

  • LVM

Volumegroups systemvg and xenvg, Size: rest of available space

  • System-Volumes-Dom0 [/, /tmp, /var, /var/lib/xen/save] fs: ext3
  • DomU-lvms added when needed


DomU MAC Adresses

Xen domUs have the MAC-Addresses in 00:16:3e:*:*:*. To avoid collisions in MAC adresses one can take the IP of the domU A.B.C.D and use the hex values for B,C and D. The following command might be usefull:

printf "00:16:3e:%02x:%02x:%02x\n" {B,C,D}

replace B,C,D accordingly.