The new Server Instant Replay feature keeps a golden copy of each operating system (OS) and then uses snapshot pointers for each physical server pointed to the SAN to keep track of things, like registry or dll changes, in the case of Windows. Once the operating system is loaded onto the Compellent SAN, a new wizard, now included with the software, walks users through the process of pointing their server to the correct operating system golden copy boot volume.
Compellent claims that the majority of its 500-plus customers use boot from SAN capabilities, which it has offered since the first generation of its product. The company also estimates that typically, boot-volume provisioning takes SAN administrators about eight hours.
It's really more like three hours for a typical setup, according to Steve Tilton, manager of networked systems for the Maine Public Broadcasting Network. The network currently has 26 servers, about half of them running Windows Server 2003 and the rest running Netware, Windows NT 4 and Sun Solaris, which it already boots through two Compellent SANs in Bangor and Lewiston, Maine.
Still, he said, "Not having to take the time every single time you add a server to configure the Microsoft OS could conceivably cut our setup time in half."
Another user, Nick Colakovic, director of IT for First Industrial Realty Trust Inc., headquartered in Chicago, said the consolidation of boot volumes will save him a total of 1 terabyte (TB) of storage space over two locations when all is said and done. The company has a 16 TB capacity on the company's main data center SAN in Mount Prospect, Ill., and 11 TB at its corporate headquarters in downtown Chicago. "Our standard allocation for a boot volume is about 10 GB," he said. "If you multiply that times 55 servers, which is the number we have, it's not an inconsequential savings for us."
First Industrial's headquarters is located right next to the Sears Tower, and the company's IT infrastructure has been designed with that building's potential for disaster in mind. The company's headquarters is actually the secondary data center for this reason, Colakovic said, and the two sites use Compellent's replication features to synchronize data nightly for disaster recovery purposes.
When it comes to the boot-from-SAN consolidation, Colakovic said another big benefit for him will be the potential change in recovery time rather than setup time. "Having to pull the entire server image over the wire for every server and then add all the changes for each boot volume could triple our recovery time in the event of a failure," he said.
Storage/operating system partnerships?
"I'm very positive about boot from SAN, especially to improve availability and recovery, and at the alternate site," said Stephanie Balaouras, senior analyst with Forrester Research Inc. "But I'm also aware of how complex it is -- it requires the proven interoperability of a lot of components beyond the array -- and partner and technology agreements and cooperation are critical."
Compellent, however, would beg to differ. "The solution doesn't require that we have agreements with server/OS vendors," argued Compellent spokesman Rob Davis. "Part of Storage Center's code is based on Java to allow us to talk to servers of any OS. Then we take advantage of the server's native failover -- a part of the OS. If a new OS were to come out, we would issue a patch to Storage Center so that the SAN would automatically recognize those servers as well."
But Balouras argued, "it will only be a meaningful announcement if they come to market with partners who support the solution. I'd want to see Microsoft and VMware at a minimum given the proliferation of server virtualization."
Calakovic said the lack of formal support agreements between Compellent and Microsoft doesn't bother him. "What does that actually mean?" he asked. "It becomes a metaphysical issue -- the only real issue would be I/O timeout on a boot volume, but if the storage performs reasonably well, that's not a problem."
Still, Calakovic said, the lack of support from Red Hat Inc. for boot from SAN for his Linux hosts has at times proved a hassle. "It still works fine," he said. "There's just a lot of manual refinements you have to do on Red Hat to set it up on a SAN because of Red Hat's reticence to support boot from SAN, which I think is childish."
Red Hat's opposition to boot from SAN is publicly documented; the company will only formally support boot from local disk.