Microsoft has made available a whitepaper that discussed the concept of booting from SAN:
“Booting from a storage area network (SAN), rather than from local disks on individual servers, can enable organizations to consolidate their IT resources, minimize their equipment costs, and realize considerable management benefits by centralizing the boot process. This white paper covers boot from SAN technology as deployed with Microsoft® Windows Server 2008 and Microsoft® Windows Server 2003. It describes the advantages and complexities of the technology, and a number of key SAN boot deployment scenarios”.
This is something we’ve done at my last two jobs using HP Blades and SAN/Ethernet Virtual Connects (VC). All the SAN and Ethernet connections come into the back of the chassis into the VC’s. There you define the networks and SAN connections. You build a profile for each server that defines which cable/logical connection is presented to each physical interface on the server. This profile is mobile, i.e. you can move it from one server to another with the click of a button. In the VC, the profile defines the WWN and the MAC addresses that the SAN fabric and Ethernet will see instead of the ones that are physically assigned to the server. This virtualises the connections allowing for mobility of the profile without compromising access to the connections, e.g. Ethernet ARP tables remember the VC profile (for the blade) MAC address and not the Blade server’s MAC address and the SAN fabric is set up using the VC profile (for the blade) SAN WWN.
Now I configure the blade to boot from it’s SAN HBA mezzanine card instead of the internal SCSI. I prefer QLogic over Emulex; I had a very high failure rate with Emulex in the previous job. That requires setting up a disk in the SAN which will be the boot disk. This disk is only presented to the server … via the WWN defined in the profile in the VC … which is what the SAN will see the HBA using thanks to the VC virtualising the communications. I install the OS and that is set up on the SAN disk. The blade has no internal disks. It’s now just a dump replaceable appliance with no data.
Why do this? Well, as I said the server is now an appliance. Other than its capital value it has no other value to the business, unlike a server that contains disks internally and whose physical MAC and WWN are presented to the network/SAN. Replacing the traditional server with new hardware is a big ordeal involving lots of downtime. For me, I can either keep a hot spare server or get HP to bring in a replacement (in 4 hours). If I keep a hot spare I can log into the VC and move the profile of the failed server over to the hot spare and boot it up via ILO. It then becomes the old server; the OS is on the SAN, the WWN and the MAC are defined in the VC profile and I’ve moved all definitions and connections over to the new server via the VC profile. Alternatively I can pull out the old server and insert a new one. the profile is associated with a blade enclosure bay. The new server then becomes the old one automatically.