HP NetServer Rack Storage 12/FC ISS Technology Update, Volume 9, Number 6 - Page 4

The iLO user interface System-specific Sensor Data Records (SDRs) determine which thermal sensors the iLO user interface (UI) displays. The Intelligent Platform Management Interface specification defines the Sensor Data Repository, which houses SDR's. The system BIOS transfers the Sensor Data Repository to iLO during POST. iLO consolidates data from a group of similar sensors (DIMMs for example). In aggregate readings, SDRs send the temperature of the warmest component in a group to the iLO UI. Other sensors may send a ―remaining temperature margin‖ reading to the UI. iLO uses this information to tailor cooling for the system configuration. Findings during development We made some interesting observations during Sea of Sensors technology development, some of which are: Running fans ―too slow‖ can result in increased power draw because of the inherent behavior of motors at slow speeds. Running some fans ―too high‖ can decrease direct-attached storage performance if fan vibration couples with disc drive rotation. Although fan failures are rare, turning off fans to save power will not allow iLO to monitor them for failures and other conditions. An unpowered fan can ―turn and re-circulate hot air. Poorly balanced fan flow rates can produce an eddy (recirculated hot air), degrading cooling performance. Additional resources Resource ―HP ProLiant Intel-based 300-series G6 and G7 servers‖ technology brief URL http://h20000.www2.hp.com/bc/docs/support/SupportManual/c0 0502616/c00502616.pdf HP Smart Array optimizes Video on Demand performance Video on Demand (VOD) is a challenging storage application area because content providers must deliver hundreds of video streams simultaneously and without interruption. The VOD servers that deliver these services require large amounts of relatively high performance disk storage. The ProLiant Smart Array team has been making important advances in the use of HP technology to optimize storage for VOD applications. Understanding how VOD servers interact with storage Optimizing for large block random I/O VOD servers stream files in a rotational manner, reading and delivering a block from one file and then another. As a result, VOD servers access the storage as random I/O-although it is random I/O with a pattern. High-performance VOD application servers use large block requests, typically 512 KB to 4 MB. This allows the servers to grab enough data from the disk to fill the video stream until the next access window opens in the rotation. The best VOD performance is gained by tuning the drive array, the file system, and the VOD application server so that each block request is stripe-sized (a full stripe width) and stripe-aligned (aligned to stripe boundaries). Many VOD implementations use Linux because it can support file systems that you can configure for stripe-aligned block requests. VOD latency requirements In storage terms, latency is the time it takes for a Smart Array controller to retrieve a block of requested data from a logical drive and deliver it to the application. With VOD, it is more important to have consistent latencies and a low maximum latency. Engineers configuring VOD servers gladly trade off a slightly higher average latency to keep the maximum latency below a given threshold. For example, VOD server performance may be OK if the latency is 70, 80 or 90 milliseconds as 4