HADR Brings Resiliency to Virtualization

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Scalent Systems

Scalent Systems' software is not storage virtualization software, nor network virtualization software, nor deployment software: It's an integrated platform that enables admins to quickly and easily deploy, move, repurpose, and clone server instances, automatically changing network settings, storage and LUN settings and more to reflect the needs of each system. By integrating control of your network switches, storage switches, storage hardware, and virtual environment into a single console, it provides flexibility and capabilities that are hard to imagine if you're used to a standard hardware-based environment.

Scalent uses the capabilities of VMware 3.5 to create instances that boot from SAN, then makes those instances completely portable. As such, you can move a server OS from a physical instance to a virtual instance, to a virtual instance on another VMware server, and even back to a physical instance, all without ever having to copy files or change any settings manually.

Suppose, for example, you have a Windows 2000 instance running in the test network. With the development finished, you might have a requirement to move it to the production network. In a typical hardware-based scenario, this would involve changing many settings internally on the server -- and possibly moving the server hardware, or at least changing the physical network connections to a different switch.

With Scalent, you would simply drag the icon from one group to the other. The system would then automatically change the VLAN settings on the appropriate switch, the network settings on the server instance, the LUN masking and other storage settings, the VMware partitioning, and virtual name of the HBA for the server instance, and the server would be in its new role. (You do need to change the HBA that the boot-from-SAN image is linked to.) No files actually have to be copied anywhere. Each server needs to have a lightweight agent installed, but it has minimal impact on the system.

Because storage replication features can be used to keep the boot-from-SAN images up to date in a backup datacenter, switchover time is very quick, limited to the time it takes the OS to boot from the new SAN image in the new location (typically faster than booting from a local disk).

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.

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