HP Smart Cache for DAS solutions

First of all, HP SmartCache is deployed and managed through the same management tool for HP Smart Array – the ACU

SmartCache is a controller-based read caching solution in a DAS environment that caches the most frequently accessed data ("hot" data) onto lower latency SSDs to dynamically accelerate application workloads, it is available on All HP Proliant Gen 8 servers.

SmartCache uses a caching architecture where a copy of the data resides on the hard disk drive as well as on a lower latency device that is used for caching. The basic HP SmartCache architecture is comprised of the following three elements:

• Bulk storage: The first element is the bulk storage device, which can be either HDDs or connections to SAN storage.

• Accelerator: The second element, the accelerator, is a faster/lower latency device that caches data. The capacity of the accelerator is less than the capacity of the bulk storage device.

• Metadata: The final element is metadata, information held in a relatively small storage area that maps the location of information residing on the accelerator and bulk storage devices.

The direct-attached HP SmartCache solution includes the three elements of the HP SmartCache architecture; HDDs serving as bulk storage, SSDs as the accelerator, and Flash-Backed Write Cache (FBWC1) memory for storing the metadata

For this implementation, the SmartCache control layer resides in the firmware of the onboard Smart Array Controller of the HP ProLiant Gen8 server, below the operating system and driver. This allows caching for devices connected to a single array controller.

HP SmartCache offers flexibility in creating logical disk volumes from hard disk drives:

• The accelerator or cache volume is designed to support any RAID configuration supported by the Smart Array controller.

• Each logical disk volume can have its own cache volume or none at all.

• Cache volumes can be created and assigned dynamically without adversely impacting applications running on the server.

Only SSDs can be used for cache volumes, and a cache volume may be assigned only to a single logical disk volume. The HP SmartCache solution consumes a portion of the FBWC memory module on the Smart Array controller for metadata. To ensure sufficient storage for accelerator and metadata, we recommend:

• 1 or 2 GB of FBWC memory or

• 1 GB of metadata space for every terabyte of accelerator space

When using the HP SmartCache solution for direct-attached storage, legacy cache is still present and operational and utilizes the remaining space in the FBWC memory. When using HP SmartCache, we recommend setting the legacy cache for 100 percent write operation. This allows write-back support on the Smart Array controller, which accelerates write performance. This also allows SSDs configured as HP SmartCache volumes to provide much larger read cache.

Source HP white papers