HP Smart Array Controller technology, 4th edition

Storage pathway redundancy

Dual Domain support for SAS creates redundant pathways from servers to storage devices. These redundant

paths reduce or eliminate single points of failure within the storage network and increase data availability.

Dual Domain SAS implementations can tolerate HBA failure, external cable failure, expander failure, or

failure in a spanned disk (JBOD).

SAAP-enabled Dual Domain is available on the P411 and P812 Smart Array controllers (SAAP license key

required) when used with the HP StorageWorks D2600 or D2700 Disk Enclosures.

Other controllers do not support SAAP, but do support Dual Domain (no license key required). For example,

the P700m Smart Array controller attached to either the HP StorageWorks 600 MDS or the HP

StorageWorks 2000sa MSA storage enclosure supports Dual Domain. For these configurations you must

install two HP 3G SAS BL Switch modules in a c7000 or c3000 blade enclosure.

Dual Domain support is available for the 3 Gb/s HP Smart Array P800 when attached to an HP

StorageWorks MSA60/70 with the HP Dual Domain I/O Module Option. Dual Domain support requires

HP Smart Array firmware v5.10 or higher and dual-port SAS drives.

Video on Demand (VOD)

Servers delivering video streaming services typically require significant amounts of disk storage. The HP

Smart Array engineering teams have made significant strides in using HP technology to optimize Smart

Array-based storage for VOD applications or any latency-dependent data flow. These improvements include

optimizing for large block random I/O and decreased maximum latency.

Optimizing for large block random I/O improves the application server's ability to grab enough video data

on each pass to maintain all the video streams in a rotating data retrieval scheme where a large number of

simultaneous video streams exist. VOD performance improvement during this operation is a result of tuning

the drive array, the file system, and the VOD application server so that each block request is stripe-aligned.

Decreasing the maximum latency of block requests to the Smart Array is one of the key goals for VOD.

Physical Drive Elevator Sorting lets the controller re-order block requests to the physical drives to minimize

the drive seek time. While this improves total performance, it can increase the maximum latency. The

controller may schedule the execution of an earlier block request behind subsequent requests and execute

the requests outside the VOD server’s required time window. Turning off Physical Drive Elevator Sorting

decreases the latency variability, which is what the VOD software wants. In a related manner, disabling

Monitor and Performance and extending the Background Surface Scan Interval help eliminate spikes in

latency that might occur during these background tasks.

Other improvements include changing the cache ratio to be 0 % read and 100 % write. Since VOD

operations are 99% random, any read-ahead operation would penalize performance. You want to post the

writes so that they have the least impact on the reads. We also found that in a multi-stream environment like

VOD, the queuing mechanism in SAS drives delivers significantly better performance than SATA drives.

Another important way to optimize VOD performance in Smart Array-based storage is to enable Degraded

Mode Performance (DPO). This decreases changes in latency between normal and degraded modes of

operation. We added DPO specifically for VOD.

Storage management

HP Smart Array controllers include built-in intelligence to improve data storage management. This makes it

easier for administrators to configure, modify, and manage storage. HP provides six utilities for managing

an array on a Smart Array controller:

 The Array Configuration Utility is the main configuration tool for HP Smart Array controllers. It exists in

three interface formats—the ACU GUI, the ACU CLI, and ACU Scripting. All three formats have separate