How to use iSCSI volumes with LVM on boot

SLES 10 SP1 - See the following article in Cool Solutions:

SLES 10 SP2 and Later

Configuring LVM Auto-assembly on iSCSI Devices

Using LVM over iSCSI on SLES 10 SP1 has the initial problem that iSCSI is started only after the network and with that far too late for the boot.lvm script to activate any LVM volume groups devices. However, with SLES10 SP2 we've integrated the necessary tools to integrate lvm startup into udev, so that any LVM volume groups will be activated automatically via udev once all required physical volumes have been detected.

1.1 How to configure

   1. Use the script /usr/share/doc/packages/lvm2/lvm-vg-to-udev-rules.sh. It takes as an argument the logical volume name, from which it discovers the volume group name that will be started automatically. This script will generate the required udev rules.
   2. Restart iSCSI; the volume groups will be activated automatically.

That's all. If you want to have the array started automatically on boot you have to switch the iSCSI component devices to 'automatic', so that the initiator will log into the target automatically on boot.


1.2 Grubby details

LVM auto-assembly in udev makes use of the udev helper program 'collect'. This program takes as the first argument an abstract 'ID' to be checked, followed by a list of component IDs. Once this program has been called with each of the component IDs as the first argument it'll return 0.

So for auto-assembly we register the physical volume UUIDs for the given volume group as argument list for 'collect'. udev (or rather vol_id) is capable of detecting the physical volume UUID on a device and hence it can be passed as the first argument to 'collect'.

Once 'collect' has been called with all physical volume UUIDs (IE udev has received events for all component devices) the next rule triggers which just calls 'vgchange -a y <vgname>' and the volume group will be activated.