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5/12/2009
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DAS VS. SAN - High Capacity

Continuing our examination of the resurgence of direct attached storage (DAS), in this entry we look at the ever-increasing internal capacity of DAS in servers. One of the key reasons users begin looking at a SAN or NAS is when the capacity demands of a single server outpace its internal storage capabilities. This may no longer be justification enough to make the move to networked storage or to continue to expand the network storage you have.

Continuing our examination of the resurgence of direct attached storage (DAS), in this entry we look at the ever-increasing internal capacity of DAS in servers. One of the key reasons users begin looking at a SAN or NAS is when the capacity demands of a single server outpace its internal storage capabilities. This may no longer be justification enough to make the move to networked storage or to continue to expand the network storage you have.What has made DAS more viable in the "can you get enough" challenge is obviously higher capacity hard drives and the increasing adoption of the 2.5" form factor. The combination allows for very dense packaging. 2.5" drives in particular allow for configurations that can offer either reasonable performance with lower capacity or very high capacity some performance sacrifice.

On the performance side Seagate for example with its Savivio 15k.2 drive can deliver a drive running at 15k RPM and a capacity of 147GB. Using the Intel 5500 based servers as a minimal reference point, a 1U server can support 8 of these drives for 1.1TB's of reasonable performance storage. All these drives are SAS 2.0 based running at 6.0Gb/s.

Of course if that is not enough performance then as discussed in our last entry, DAS VS. SAN - Capacity And Performance Management, 400GB's of PCI-E Solid State Storage can also be had for less than $15k.

The capacity side of things is just as interesting. The Seagate Savvio 10k.3 2.5" drive comes in capacities up to 300GB's running at 10K RPM, allowing for 2.4TB's of capacity in that same 1U box. Obviously there are larger servers available that have a higher drive bay; for example there are 2U servers with up to 24 2.5" drive bays for 7.2TB's in a single server.

The net is with DAS storage for mainstream applications you can get the performance or capacity you need but it may be difficult to get both. The storage decision in a DAS world becomes very application specific.

From the SAN side, when the time is right many of the SAN storage systems will switch to 2.5" drives, and they will pick up the same capacity densities that server storage enjoys today. Right now 2.5" drives are still priced at a slight premium over 3.5" drives and other than power savings there are limited compelling reasons to make the switch.

The final area we will explore in our DAS vs. SAN series is efficiency. While SAN can, in most cases, out perform and out scale DAS, its in the area efficiency where it should have the biggest advantage and provide the biggest benefit. Or does it?

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George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.

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