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Re: [Xen-users] Does XCP support network boot/diskless dom0?

Dave Scott wrote:
either PXE or iSCSI.  I am investigating a move to XCP at our next
hardware refresh and going diskless with the dom0s would nice.

Not yet...

I believe Alex [cc:d] has some early prototype code which enables this kind of 
thing. Alex, could you describe what it can do/ roughly how it works?


Hi Dave/Matt,

The diskless support that I have been working on is based on booting an iSCSI disk. Accesses to this disk is via a software initiator.

Both dom0 and the host-installer need to be told what disk to access and how to access it. This is done via the iBFT (iSCSI Boot Firmware Table) in low memory. This table is either written by the BIOS (if the BIOS supports boot from iSCSI), or by a boot ROM in a NIC (if there is a NIC that supports boot from iSCSI), or even by a PXE network boot program like gPXE. However, NICs listed in the iBFT are reserved for root disk access and cannot be used for management or by VMs.

If you don't have a BIOS that supports boot-from-iSCSI it can be quite tricky to set up a PXE server with the right configuration so that the diskless servers download the correct gPXE binary which sets up the iBFT correctly before running the host-installer or booting the iSCSI LUN. For this reason, I've created an appliance VM which I'm calling the XenBootServer. This provides an ncurses UI for commissioning new diskless XenServers and provides the PXE server, online install media, and answerfiles for you. All you have to do is answer a few simple questions.



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