InfoWorld — Virtual appliances are great for the same reasons physical appliances took the IT world by storm: They make deployment a snap -- even instantaneous -- while at the same time reducing costs. It's a formula that made hardware-based appliances immensely popular for network security, backup, storage networking, file services, email, and many other single-focus solutions.

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By leveraging open source solutions, and shedding the hardware entirely, virtual appliances can push the cost savings to whole new level: completely free. You'll find an increasing number of open source projects available for download in virtual machine formats for Xen, VirtualBox, VMware (VMW), and other virtualization platforms. Naturally, the virtual appliance is especially handy when the solution stitches together a host of components or relies on an entire LAMP stack. Why build it yourself when you can download the whole installation, already pre-configured?

[ Two of these projects -- Cacti and FOG -- are InfoWorld Bossie 2010 Award winners. Read about the other InfoWorld Bossie 2010 winners in "Bossie Awards 2010: The best open source software of the year." ] 

In short, with the rise in popularity of virtualization and server consolidation, IT pros have many other options, options that offer all of the pros of a physical appliance, with very few of the drawbacks. Even when the software is proprietary, a virtual appliance costs less than a physical hardware appliance. And then there are all the other advantages of virtualization: The ability to run multiple virtual appliances on a single server, the ability to migrate virtual appliances from one server to another, and the ability to back up a virtual appliance almost instantly. All of these capabilities play well into disaster recovery and business continuity planning and help make virtual appliances a "must consider" technology for businesses large and small.

Before diving into the widening world of virtual appliances, there is no better way to experiment than with virtual appliances that are free to use and meet unique needs in an enterprise. Listed below are some of the free standouts that we have come across over the years, all of which offer enough features and capabilities to make the transition from an experimental virtual appliance to a line-of-business solution.

Openfiler NAS and SAN Openfiler is a full-fledged NAS/SAN appliance (or IP storage gateway) that can be downloaded as a virtual appliance for VMware and Xen hypervisors directly from openfiler.com. Openfiler offers storage administrators a set of powerful tools that are used to manage complex storage environments. The product brings reliability to storage with support for both software and hardware RAID, monitoring and alerting facilities, and volume snapshot and recovery features. High availability is included in the form of active/passive clustering, multipath I/O, and block level replication. Scalability is also addressed by a filesystem that can support up to 60TB, with the ability to expand filesystems and volumes without taking storage offline. High performance is guaranteed by a Linux 2.6 kernel that supports the latest CPU, networking, and storage hardware.

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