HP SmartCache technology

Technical white paper | Product, solution, or service
5
HP SmartCache for Direct-Attached Storage
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 (FBWC
1
) memory for storing the metadata (Figure
3). 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.
Since the HP SmartCache solution is implemented within the Smart Array firmware, this solution can be used on any
operating system supported by ProLiant servers. The HP SmartCache solution operates transparently, without any
dependencies on operating system, device driver software, file system type, or applications.
The initial release of the HP SmartCache solution supports write-through caching. When an application writes data to the
disk, the Smart Array controller writes the data to the HDDs and if the data is also in the cache volume, the data is written to
the SSD.
1
FBWC: Flash Backed Write Cache, an integrated persistent memory device used for caching operations conducted within the Smart Array
controller’s firmware. Writes are posted to the FBWC, acknowledged immediately, and later are completed to the actual hard disk drives
for improved latency of write operations.
Figure 3.
HP SmartCache can be applied to direct attached storage.