A rack power distribution unit (PDU) is mounted in an IT equipment rack and provides electrical power to various IT devices such as servers, routers, firewalls, etc. Today, PDUs come in a number of configurations that help you manage power in the data center. Here we will describe the four basic types and provide you with a summary or their strengths and weaknesses.

Types of rack PDUs

• Basic PDUs
  • Summary: Basic PDUs are power strips that are constructed out of high-quality components for use in critical environments. They generally support distributing correct voltage and current to several outlets. 
  • Pros: Basic, affordable, proven technology.
  • Cons: Lack instrumentation and are not manageable on any level.
• Metered PDUs
  • Summary: Metered rack devices typically meter the power draw, i.e., current, at the PDU level, and display it locally. A few sophisticated models have user-defined alarming capabilities and the ability to remotely access PDU-level metering data over a serial or network port. 
  • Pros: Provide real-time monitoring of PDU current draw. In some cases user-defined alarms alert IT staff of potential circuit overloads before they occur.
  • Cons: Most only provide information locally and do not offer critical environmental data or outlet-level monitoring or switching.
• Switched PDUs
  • Summary: Switched PDUs provide controlled on/off switching of individual outlets and load metering (see metered PDUs above) at the PDU level. They typically allow users to power recycle devices remotely and apply delay for power sequencing and provide some outlet use management.
  • Pros: Remote power on/off capabilities, outlet-level switching and sequential power-up.
  • Cons: Lack temperature and humidity monitoring. The information provided and functions supported are limited.
• Intelligent PDUs
  • Summary: An intelligent rack PDU can be controlled remotely via a Web browser or command line interface (CLI). It meters power at both the PDU level and the individual outlet level; supports alerts based on user-defined thresholds; provides security in the form of strong passwords, authentication, authorization and encryption; and incorporates rich environmental management capabilities. Models should also be highly customizable, support the industry’s latest standards-based techniques like SNMP TRAPs/SETs/GETs, IPMI and SMASH CLP, and integrate seamlessly to existing corporate infrastructures like LDAP, Active Directory®, RADIUS and NFS servers. 
  • Pros: State-of-the-art devices, they are remotely accessible via Web browser or CLI. Models include all the features of switched devices (remote power on/off capabilities, outlet-level switching and sequential power-up), plus offer real-time environmental data, standards-based management, integration with existing directory servers, enhanced security and rich customization.
  • Cons: Higher cost relative to basic and metered PDUs due to their greatly enhanced feature set.

Benefits of an intelligent rack PDU

Dominion® PX, Raritan’s family of intelligent PDUs, provide real-time, outlet-level and PDU-level power monitoring, remote outlet switching, and rack temperature and humidity monitoring. They help IT administrators and facilities managers improve uptime and staff productivity, efficiently utilize power resources, make informed capacity planning decisions, and efficiently utilize energy to save power and money. The metering capabilities enable steps towards becoming a more green data center.

• Improve uptime and staff productivity
  • Monitoring power at a PDU level, with user settable thresholds and alerting via e-mail or SNMP, provides awareness of potential issues before they occur. 
  • Remote reboot of servers and IT equipment from anywhere in the world via a Web browser to improve uptime and productivity.
• Efficiently utilize power resources
  • User configurable outlet-level delays for power sequencing prevent circuits from tripping from IT equipment in-rush currents.
  • Keeping outlets off and provisioning outlets only when needed prevents IT equipment from being plugged in to circuits that are already heavily loaded and are at risk of tripping circuit breakers.
• Make informed capacity planning decisions
  • Even if a data center appears to be out of power capacity, outlet-level monitoring may identify some simple rearrangements of IT equipment to free up power resources by balancing power demands across racks.
  • With PDU-level monitoring it is easy to set thresholds so you know when you’re getting close to circuit limits. With outlet-level monitoring you can identify the equipment that needs to be changed to stay within the margin of safety.
  • Temperature sensing and environmental profiles are important when a data center is rearranged, which can lead to counterintuitive changes in temperature. For example, it is not uncommon for air conditioning units to be added to a server room only to discover that, due to changed air flow patterns, some racks receive very cold air while other racks are actually hotter than before the extra air conditioning was added.
• Save power and money
  • By using outlet-level power monitoring combined with trend analysis, individual servers can be monitored and those that constantly run at 30% of peak power are candidates for virtualization or decommissioning.
  • Remote power cycling saves money as IT managers can quickly reboot hung or crashed servers and IT equipment without having to incur the cost of site visits.
• Take a step towards becoming a more green data center
  • A common data center mistake is overcooling IT equipment. While it is true that excess heat can shorten the life of IT equipment or even cause it to fail, excessive cooling does not prolong equipment life and is wasteful of energy. Temperature and humidity sensors help data center managers optimize their air conditioning and humidification settings and improve efficiency.