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Cloud compute infrastructure

Other key drivers for the revival of DAS are the designs of massive storage environments like those of Facebook, Google and others. These systems combine compute and storage on a single server that’s highly networked for communication with the other servers. These systems often have locally attached storage and the ability to access data on other servers. They can even leverage a combination of PCIe SSD and hard disk drive (HDD) for booting. These online providers and Internet technology companies chose this design so they could get incredibly cost-efficient architectures with the ability to scale easily as new servers were added.

This model of DAS converged with compute was thought to be a limited use case, one that only companies with large online apps would deploy. Now, however, thanks again to server virtualization, there’s often a need to build scalable compute and storage infrastructure simultaneously. Vendors like Nutanix offer products that are clusters of servers with internal storage to provide a turnkey cloud compute-type of infrastructure suitable for more traditional data centers.

Server virtualization still needs shared storage to move virtual machine images and provide high availability. These converged architectures automatically copy data to the other nodes in the cluster so that the virtual machines’ images are available to any node in the cluster. This “shared DAS” model provides the simplicity

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and cost effectiveness of local storage while providing many of the benefits of a SAN.

If DAS lives, is SAN dead?

DAS isn’t just living, it’s thriving. There are many storage experts who believe the data center is moving toward a “DAS mostly” environment, as described above, where the SAN would become the long-term repository while truly active data gets stored locally on the server that needs it. The software to manage this movement of data is maturing quickly and will be used to keep active data locally. It will also be able to acknowledge the writing of new data locally and then sync that data to the capacity SAN in the background.

The drivers for a potential shift to this “DAS mostly” model are the performance demands of the virtual environment and the performance capabilities of solid-state storage. One driver has a need for data locally and the other has the ability to leverage local data by avoiding the latency caused by the storage network.

Still lots of storage options

As always, there are a lot of potential options for a storage administrator when dealing with storage challenges. The first step is to invest in a performance analysis tool that can help fine-tune the current environment. This maximizes the current investment and allows for an informed decision when selecting what step to take next.

If the network or storage infrastructure can’t be upgraded due to budget or time constraints, then a valid approach would be a strategy of mixing SSD-based DAS with SAN storage. This would provide the benefit of improved performance by eliminating the storage network bottleneck for maximum SSD benefit.

If a refresh is in the budget, an investment could be made in storage network infrastructure and a shared storage system, such as an all-flash device to eliminate storage performance concerns for the foreseeable future. Still, with this approach, using SSD DAS as a booting and paging device can complete the storage performance picture.

BIO: George Crump is president of Storage Switzerland, an IT analyst firm focused on storage and virtualization. 

This was first published in May 2012

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