Enterprises have long struggled with the storage conundrum of high capacity vs. high performance. Hard disk and solid state drives (SSD) each offer advantages the other cannot match. Hard drives are the reigning kings of capacity, but lack the performance, ruggedness and power-saving features of SSDs. For all their advantages, SSDs are miles away from hard disk drives in delivering the capacity and cost-effectiveness required by enterprise applications.
Offering such varied but compelling attributes, these two technologies are making tiered storage a relevant and highly logical approach to managing data. It just makes sense to combine the best of disk- and flash-based technology within one enclosure, and now a new category of tiered storage called real-time tiering finally does just exactly that.
The administrative challenge with automated tiered storage is ensuring the hottest data is on the SSD level at all times. With a dynamic workload that is often presented by multiple virtual machines, this is no easy task. With virtual server environments, applications are responding to changing activities, resulting in an unpredictable and ever-changing workload on the storage. Real-time tiering in the storage array tackles this data-allocation challenge, taking automated tiered storage to a new level by ensuring the most critical data always reside on SSDs, while less active data blocks are moved to the hard disk drive tiers.
Autonomic, real-time tiering with SSD drives and built-in virtualization overcome the two major limitations found in most tiered storage systems today. By automating the migration of data in real-time, the storage system virtualizes both the SSDs and hard disk drives at the sub-LUN-level across multiple RAID sets. Intelligent algorithms continuously monitor I/O access patterns and automatically move hot data to the SSDs to maximize the speed of I/O operations and, therefore, improve performance of the aggregate application workload.
So when a Web server, for example, experiences a rush of high volume activity based on the latest social trends, real-time tiering ensures the hot data is handled by the fast SSD drive tier. As the trend fades, a SAS hard disk drive tier houses "warm" data, and as activity continues to decrease, "cold" data is moved to an archive layer consisting of near-line SAS disk drives. All of this is done in real time, automatically and seamlessly, without any need for intervention from administrators.
Real-time tiering goes beyond automated tiering alternatives
Traditional automated tiered storage offerings suffer from two common and sometimes significant limitations. The most crippling is insufficient frequency of data migration between tiers. Many SAN solutions are capable of moving data to the SSD tier on a daily basis only owing to the disruptive nature of the migration itself. Because halting an application to migrate the data is normally unacceptable, the migration must occur during periods of minimal or no demand, which is usually overnight. Such a daily or nightly migration may be sufficient for applications where the datasets can be known in advance (and fit entirely in the SSD tier), but it is of little or no value for all other applications where the most active data changes throughout the day.
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