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Add pci hot-plug in images for Openstack.
We use Openstack Diablo release on fedora. To fully use openstack nova-volume service you need to add PCI hot-plug feature in guest system. It will allow to attach and detach volumes without reboot. Linux Kernels support this feature with acpiphp module.

Ubuntu:

We need to load acpiphp module. To load it automatically after reboot

 echo “acpiphp” >> /etc/modules

Tested on Ubuntu 11.04, 11.10.

Fedora:
I have use libvirt VMs and by default there is acpi=off kernel parameter. To allow pci hotplugging remove acpi=off from kernel parameters by editing /etc/grub.conf. Tested on fedora 14, 15

CentOS:
Simplest solution it is add “modprobe acpiphp” string in /etc/rc.local. Tested on CentOS 5.6

echo “modprobe acpiphp” >> /etc/rc.local

How to attach volume in OpenStack:
To create 1GB volume with euca2ools and attach it to instance:

euca-create-volume -s 1 -z nova

euca-attach-volume -i i-00000043 -d /dev/vdb vol-00000003 

To see disk in guest system:

fdisk -l 

All works good, if you can attach, detach and again attach volume to instance.