We examine five products that marry high availability and disaster recovery to your virtual server environment
The level of flexibility that Scalent offers, in terms of being able to run an OS instance either on hardware or any VMware server available, is especially noteworthy. Often with other failover systems, the two servers need to be identical to ensure that VMware drivers for CPU type, motherboard type, VMware partitioning, network settings, and capacity all match between the two. With Scalent, the backup server doesn't have to match the original. Scalent does a full install of the OS instance with all drivers, so images will work on any hardware. Some Linux display drivers may need to be re-configured, but that is easily done.
Using Scalent, high-availability environments are also easy to create and maintain, since it's simple to clone a boot image and create multiple instances, either on the same or separate VMware servers. Scalent can even work with load balancers such as F5's Big/IP to add new instances to a load balancing cluster.
Installation is a complex business. Scalent will integrate with your existing storage and network hardware, but may have to do on-site installation and configuration to get everything working, depending on what hardware you have. For the review, the company provided a complete rack of preconfigured equipment including an Ethernet switch, FC switch, storage system, and five servers, in addition to the server running the Scalent software.
In very short order, I was then able to add a new server (an HP ML370G5) from my lab to the provided pod. Using the Scalent software, I created a VLAN, connected the pod to my network, logged in to the HP server, added the lightweight agent, connected the HP to the Scalent controller, and added the server to a managed group in about 15 minutes total. Then the Scalent appliance deployed OS instances to the VMware ESX 3.5 server in less than a minute.
Scalent also supports iSCSI boot from SAN using emBoot, which means that iSCSI boot from SAN doesn't require a specialized (and expensive) TOE network interface card. Using iSCSI rather than Fibre Channel is transparent: Management occurs in the same fashion in either case. You could even mix both in the same environment.
Scalent is not inexpensive. The company prices in packs of managed physical CPU sockets (regardless of the number of cores); for example six dual-socket systems or three quad-socket systems. Pricing is about $1,000 per physical socket. This applies only to managed systems, and you can run any number of VMs on each system. However, given the flexibility and control provided, the cost is definitely worth it. Any large datacenter, or networks with requirements for scalability or failover, or environments with rapidly changing requirements that make regular re-purposing of systems a necessity should consider Scalent.
Stratus Technologies Avance 1.3
Stratus Technologies Avance 1.3 is a rival to Marathon's everRun VM in that it provides automatic failover. Like everRun VM, Avance runs on Citrix XenServer. Stratus sells a customized version of XenServer as part of the product, however, hardened and modified to support Avance's failover services. Unlike Marathon, Stratus supports Linux as well as Windows instances.