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CommunicationsUPS provision needs to be an integral part of the SAN strategy, not an afterthought. Monitoring and control of the UPS by the network manager is essential. This can range from software which shuts down the SAN hardware in an orderly fashion, to a fully interactive Simple Network Management Protocol (SNMP) communications (which makes the UPS an intelligent part of the hardware). This allows the network or IT manager to monitor power conditions on the hardware and be alerted instantly to any potential problem areas. Such software should be easy to use, install and integrate seamlessly with existing network operating systems.
System ConfigurationThere are four classes of power solutions designed to meet the protection requirements of most SAN hardware. These are:
- Clustered protection.
- Integrated protection.
- Facility-wide protection.
One-on-OneOne-on-one means that each SAN node which needs protection gets its own UPS. The server will have its own larger and more sophisticated UPS than the workstations or peripherals, but the one-on-one principle still applies.
Clustered ProtectionClustered protection protects all SAN nodes in a single room. In other words, it protects a "clustered" group of servers (and other network equipment) by means of a single larger UPS.
Integrated ProtectionIntegrated protection "integrates" the power protection within a cabinet enclosure or raised floor system. It is termed integrated because many protection functions are combined into one system including system control/monitoring, air conditioning, security, wire management, smoke and fire alarms.
Facility-Wide ProtectionIf nearly everyone has their own computer and SAN servers (and nodes are located throughout an office), the best solution is often a large-scale UPS, which can provide protection to an entire floor or facility. The ideal time to plan this is when a building is being newly built or restored.
TopologyUPS design can employ a number of different topologies. These include:
- Line interactive.
OfflineMost SAN hardware now uses what is known as switched-mode power supplies, which can ride out very short gaps in the main power supply, because they store a small amount of charge in their large capacitors. This means they may be able to use off-line UPS units, as there is inevitably a short switchover time (measured in milli seconds) between a mains failure and transfer to the UPS battery.
Used almost exclusively at the low end of the UPS power spectrum, offline UPSs are the simplest and most cost-effective option. They supply partially filtered main power to the load (that is, there is virtually no power conditioning), but keep a charged battery in reserve. When the main supply falls below a certain voltage level, a switch in the UPS connects the battery to an inverter, which then converts the DC of the battery to an AC supply which can be used by the SAN hardware's power supply. In terms of applications, offline UPSs are best used where the SAN hardware being protected have low power ratings and are not mission critical.