Software-defined storage extends control

You’ve heard by now that just virtualizing your servers won’t achieve maximum efficiency in your data center. Getting the maximum use out of your equipment means virtualizing all domains. But what does that mean for storage?

In the ideal data center, you’d want all the storage available for whatever application needs it the most. It is for this reason that VMware developed Virtual SAN.

Built directly into the kernel of VMware vSphere, Virtual SAN pools resources from x86 servers with solid-state drives (SSD) and hard-disk drives (HDD). The combination is designed to create fast, dependable storage that’s also easily expandable.

The solution is generating buzz in the blogosphere.

“It allows you to control availability and performance in a way I have never seen it before, simple and efficient,” writes Duncan Epping on Yellow-Bricks.

Software-defined storage

Because the use of storage is software-defined, you can use Virtual SAN with most industry standard hardware. In fact, 12 industry leaders such as Dell have agreed to certify more than 150 servers and devices with Virtual SAN.

In addition to a hardware compatibility list, VMware has announced that it will offer the alternative of VMware Virtual SAN Ready Nodes, a set of pre-configured servers to simplify configuration and procurement.

The basic requirement: Hosts must have at least one SSD and one HDD. Each write goes first to SSD and second to HDD. This combination boosts the performance of the I/O, while maintaining the ability to scale out inexpensively.

The SSDs provide a read cache and a write buffer. By keeping a cache of commonly accessed disk blocks, the read cache reduces the I/O read latency in the event of a cache hit.

Using SSD also reduces the latency for write operations. Availability policy settings ensure that all virtual machines deployed to Virtual SAN have at least one additional copy of their data, including write cache data.

After an application inside of the guest operating system initiates a write, that write goes both to the local write cache on the owning host and also to the write cache on a remote host or hosts. Before it is acknowledged, the write must be committed to the SSD on both hosts. If the host fails, the virtual machine will access the replicated copy of the data on another host.

The use of HDDs, on the other hand, allows flexibility. You can scale up, scale out or scale down just by adding more disks or hosts. That makes it easy to quickly accommodate intensive demands, such as big data. And, it saves time on testing and development.

Full release anticipated

Virtual SAN is automated as well, with policy-driven management for each virtual machine. The new Storage Policies solution offers an improvement over the original version of vSphere Storage Profiles. As in vSphere Storage Profiles, Storage Policies uses the capabilities in the policy to select an appropriate data store when provisioning a virtual machine.

But in contrast to vSphere Storage Profiles, the new Storage Policies also notifies the underlying storage layer that there are certain availability and performance requirements for a specified virtual machine.

Other policy settings stipulate the number of replicas of the virtual machine files for availability or may contain a stripe-width requirement for performance.

VMware has made Virtual SAN available in public beta, and plans a full release early this year.

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