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With the many new storage tiers that have emerged, and the price, performance and capacity attributes of SSDs and HDDs changing rapidly as new technology (such as shingled magnetic recording (SMR), 3D NAND and 3D XPoint) is developed, software-defined storage is emerging as a key enabling technology multi-layered tiered storage.
That's the view of Mark Lewis, a former CTO of EMC and GM of HP Storage and now CEO of storage software startup Formation Data Systems. That's because software-defined storage allows any type of storage, including emerging storage media types like 3D XPoint, to be attached to commodity hardware, and tiered storage functionality is provided by the SDS software itself.
"If you take the example of 3D XPoint, software-defined storage changes the game," Lewis says. "Up to now, every time a new tier of storage opened up, you had to deal with a whole new range of vendors selling incompatible hardware. But software-defined storage insulates you from new architectures and products, so there's no need to change arrays and learn how to use new storage software."
That makes it much easier to create additional storage tiers to match your data's requirements, without the costs associated with purchasing and managing new storage systems cancelling out any benefits.
But Freeform Dynamics' Tony Lock warns that although software-defined storage is a good idea, it may not be suitable for small and medium-sized organizations. "For many organizations, anything that requires implementation is tricky – they want to buy storage that is supported by a vendor."
Tiered Storage with Data Virtualization
Mark Lewis points out that many software-defined storage implementations in the past have tended to focus on the lower layers, Tiers 3 and 4, where low-use data and archive data is stored. Here a key enabling technology is data virtualization, Lewis believes. "With data virtualization, an application doesn’t know what policies you set about storage tiering. If you need data, you just get it," he says.
"With virtualized data – block, file or object – we create an index for it so we have a data object model. All these objects are structured, and the index is structured. So then we can move data from flash to disk and then on to the cloud without changing the index needed to access the data. So as far as the application is concerned, it thinks the data is in the same place."
Data Classes for Tiered Storage Layers
In order to benefit from multi-layered tiered storage, it is necessary to classify your data into multiple classes. Today most organizations use just four classes for tiered storage:
- Mission critical. This class of data that always needs to be stored in the highest level of tiered storage (Tier 1) because it is needed to support high-speed applications – perhaps supporting customer transactions. Delays in accessing data will cause the organization to lose business or otherwise negatively impact profitability. Performance is all-important.
- Hot data. This class of data needs a relatively high level of tiered storage (Tier 2) because it is in constant use in applications such as CRM, ERP or even email, and needed for the day-to-day running of a business. Performance is important at this layer of tiered storage, but cost is also a consideration.
- Warm data. This class includes older data such as emails that are more than a few days old or data on completed transactions. This type of data will be accessed relatively infrequently but still needs to be readily accessible when required. The most important consideration at this layer of tiered storage, Tier 3, is cost, but subject to a minimum performance threshold.
- Cold data. This class of data may ever be accessed again, but it needs to be archived and retained to comply with regulatory or other legal requirements, or simply because it may have some value at some unspecified time in the future. Cold data is ideally suited to the lowest layer of tiered storage, Tier 4, where access times of minutes or hours are acceptable, and low cost is the overriding consideration.
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