Servers meet storage, virtually


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IBM's view of virtual machines
That's a very different approach than IBM's, where virtual machine technology is architected as a core function of the CPU, as opposed to a kernel-level software layer, and where the file system is a separate component. Virtual machines require a CPU's support for what IBM calls micro-partitioning or dynamic partitioning: A processor can be divvied up in equal increments and assigned to work for a virtual machine.

That's in contrast to logical partitions (LPARs), as they exist on iSeries and pSeries servers, as well as Sun Solaris and HP-UX. With LPARs, it's possible to partition a symmetric multiprocessor (SMP) server's processors "logically" along processor lines. For example, with LPARs, a four-way server can have four logical partitions, explains Jeff Barnett, IBM manager of market strategy for storage software.

This spring, IBM announced its Virtualization Engine (VE) technology, which borrows the mainframe's micro-partitioning concepts, and carries them over to the Power 5 chip, which will ship this year in new iSeries and pSeries servers. Virtual machine technology built on top of VE can run on 10% increments of a processor, and virtual machines can span processor resources. In other words, a four-way server could conceivably have 40 virtual machines on it, and a single virtual machine can consume resources from more than one processor at a time.

VMware builds a file system

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into its virtual machine server directly, but IBM's approach to virtual machines keeps its clustered file system, SAN File System (SAN FS), separate. While not a requirement of a virtual server environment, "SAN FS would greatly enhance the flexibility of the system," says Barnett, in that it allows you to move data around without affecting the application. In a SAN FS environment, Barnett explains, space isn't physically allocated to individual servers, but rather "dynamically allocated on demand." As a result, virtual machines are able to move around an environment, and unequivocally access their data.

This May, IBM announced SAN FS 2.1, which added support for Solaris and Linux hosts, on top of AIX and Windows. Furthermore, it now supports "any disk environment as long as it adheres to good SCSI protocols," Barnett says. Previously, SAN FS had been limited to IBM Shark, FAStT arrays and those virtualized behind its SAN Volume Controller (SVC).

Other software components of the VE family that IBM has previewed include IBM VE Console, IBM Director Multi-Platform, Tivoli Provisioning Manager for managing workloads and IBM Grid Toolbox, Barnett says.

Management is key
Indeed, it's the availability of comprehensive management tools that makes or breaks a virtual machine environment, and not your storage environment. "What you need to worry about is the level of complexity you start to build, and how you are going to manage it," says Data Mobility Group's Webster. On the mainframe, the availability of comprehensive management functionality for virtual machines has ensured virtual machines' popularity. Virtual machines have been in use for 30 or so years, and users routinely see 80% to 90% utilization rates, says IBM's Barnett.

To achieve that kind of success outside the mainframe environment, management tools must interact with virtual machines the same way they do with traditional servers. Barnett claims that is the case with VE-powered virtual machines. "Virtual machines look like separate physical machines to the outside world," he says, ensuring smooth integration with storage resource management (SRM) tools and backup applications.

On that front, VMware may have more work to do. At least in the context of SRM, what you see is not what you get in a VMware environment, admits VMware's Raghuram. SRM tools still only see the physical component, when ideally, for predictive purposes, SRM tools also need to see the logical virtual machines. That's on VMware's list of things to do, says Raghuram. "Over time, we'd like to integrate into management standards that want to provide visibility into the entire path, from the virtual machine down to the block," which in turn would give administrators "a more granular view of how storage is being allocated" to the various virtual machines.

This was first published in July 2004

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