Your server vendor would be in the best position to provide information about iSCSI boot. This depends on BIOS support, versions of Broadcom firmware, supported drivers etc.
It is definitely working. Where it becomes interesting, when you need move the whole server to different system. There are solutions that offer automatic failover in case of server failure (including making proper LUN masking adjustments etc). The nice thing is, no changes are required in operating system or application, no cluster software.
Windows 2003 cannot be installed directly on iSCSI initiator; you need to install it on local disk, copy onto iSCSI LUN and make adjustments so that system boots. Some vendor installation tools automate it. Windows 2008 can be installed directly on iSCSI LUN; again it is best to ask server vendor about required driver versions, BIOS support etc.
to my eyes looks like assuming that simly transferring a boot image to an iSCSI target does the trick of iSCSI boot (last step says "iSCSI support is built in to Server 2008. If you are booting from iSCSI, you can immediately transfer the Windows Server 2008 disk image to your iSCSI target.")
Or am I missing something?
Or do they simply use gPXE (running, say, off USB stick) as a boot loader, which in turn loads the actual OS?
When the initiator (the "disk drive driver") initalizes, it provides "disk access" (a disk drive is seen by the OS, said disk drive being a remote iSCSI target) for the OS to continue booting (the OS does not uses int13h anymore then and gPXE can theoretically be unloaded)
Note that gPXE can be loaded from various kinds of storage, including PXE boot program, floppy boot (or floppy emulation), Boot-ROM...
I have read that some versions of Linux KVM (Kernel Virtual Machine) use gPXE as their "PXE ROM".
In order to boot WIndows from iSCSI, I think you have some other explanations here:
Just a quick update; I've successfully performed iSCSI boot of an IBM x3850 X5 server from a NetApp FAS3070. The OS is Windows 2008 R2, so the iSCSI initiator comes with it. The NIC is onboard Broadcom. The server was boot ROM enabled but I didn't need to use gPXE.
Thanks to the tips and discussions on this thread. Especially to Olaf, Andrey, Mrlevivigatt.