We’ve all become used to the concept of HA in virtual infrastructure – basically in a resource pooled environment such as XenEnterprise v4, or VMware VI3, when a host in the pool fails, its VM workload can be restarted, possibly automatically, on other hosts in the resource pool.
XenEnterprise v4 takes this concept one step further, unlike VMware with its single-point-of-failure management tool, Virtual Center. VC is a traditional heavyweight management app with a database that owns authoritative state on the managed set of hosts, and is therefore vulnerable to catastrophic failure. Tiring of hearing about IT managers asking whether we offer DR for our XenCenter management solution (something they believe is required for their VMware installations), I’m always delighted to tell them that we do for management state what we can do for VMs. In a XenEnterprise v4 resource pool, all management state for all hosts and all VMs is stored redundantly in every host in the cluster. At any time, one host is the pool leader, offering a powerful pub-sub XenAPI interface to our XenCenter management console (and 3rd party apps) that delivers notifications, performance stats and the like, and takes instructions for the pool to execute (managing VM lifecycle, for example). But if the pool leader fails … any other server in the resource pool can simply take over the job with no state loss. Just one of the cool features in XenEnterprise v4 worth a mention.
While on the topic of reliability, #1 on the list of questions notto ask me is “Is XenSource’s product really reliable?” The answer, of course is an unequivocal “yes”, based on having the same number of production users with our products as VMware has with ESX, and having never had to ship a hot-fix to date. But the answer is also changing. With the help of some friends (as you’ll learn at VMworld) the answer will soon become “it’s not only reliable, it’s fault tolerant!”. Yes, VMs that never stop, even if you stab the host through its hot silicon heart, or rip the ethernet card from its slot, sending packets flying. Skeptical? Come to VMworld where you will see the world’s first demonstration of fault tolerant VMs, on XenEnterprise v4.