HPE HP ProLiant Gen8/Gen9 Servers - SSD Smart Path vs SmartCache

a. Is it hardware based or software based?

HP Smart Path is a feature in Smart Array software stack namely the HPE Smart Array driver and is implemented only on direct-attached storage.

 

HP SmartCache feature is a controller-based read and write caching solution that caches the most frequently accessed data ("hot" data) onto lower latency SSDs to dynamically accelerate application workloads. This can be implemented on direct-attached storage and SAN storage.

b. How does it work?

HP SSD Smart Path and the normal I/O path are both active simultaneously.The Smart Array device driver coordinates with the Smart Array firmware for keeping an up-to-date map of the disk and volume layout. With this map, reqeusts are checked and qualified to bypass the Smart Array firmware and use the Smart Path. HPE SSD Smart Path qualified requests are generally small read requests for volumes of any RAID level and small write requests to RAID 0. The normal I/O path handles large requests and most writes. If a request goes through HPE SSD Smart Path and results in an error, the request is retried through the normal I/O path. If volume expansions, rebuilds, re-configurations, or RAID-level migrations are in progress, all requests use the normal I/O path.

HP SmartCache solution includes the three elements:

i. HDDs serving as bulk storage. Each logical disk volume can have its own cache volume or none at all.

ii. Only SSDs can be used as accelerator or cache volume. Any RAID configuration supported by the Smart Array controller is supported for the accelerator. Cache volumes can be created and assigned dynamically without adversely impacting applications running on the server.

iii. A portion of Flash-Backed Write Cache memory module on the Smart Array controller is used for storing metadata.

When using the HPE 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, it is recommended to set the legacy cache for 100 percent write operation thereby allowing write-back support on the Smart Array controller and  allows accelerator to provide much larger read cache. The SmartCache control layer resides in the firmware of the Smart Array Controller, it is not dependant of operating system, device driver software, file system type, or applications.

 

c. Dependencies

HP Smart Path is a default feature HP Smart Array P-series controllers

HP SmartCache requires license.

d. Operating system support - needs 

HP Smart Path

Operating Systems supported on HP ProLiant Gen 8 and HP ProLiant Gen 9 Smart Array Controllers support this technology.

HP SmartCache

Operating Systems supported on HP ProLiant Gen 8 and HP ProLiant Gen 9 Smart Array Controllers support this technology.

e. Functionality limitations

 

HP SSD Smart Path is automatically and temporarily disabled any time the disk array is in degraded mode due to a drive failure, rebuild operation, expansion, or migration.

HP SmartCache is not disabled on performing any  of the above operations.