Issue link: http://cp.revolio.com/i/809568
12 | THE DATA CENTER JOURNAL www.datacenterjournal.com whIch one IS rIght for My Server? Each of the above options has advantages and disadvantages. e list below examines various characteris- tics and details why they are impor- tant for data storage. energy density is how much en- ergy (watt-hours) you can get per unit volume and/or weight. e higher the energy density, the smaller (in size and weight) the battery that supports a given load. Lithium-ion batteries have the highest energy density (5x that of lead-acid), whereas supercapacitors have the lowest. Supercapacitors aren't meant for applications that require a lot of energy. Servers that need a long uptime on batteries (especially those that have hard drives instead of flash memory) should consider lithium-ion solutions. power density relates to how much power can be extracted per unit volume and/or weight. Servers con- sume lots of power; a 1U server can draw more than 1 kW. Supercapaci- tors offer the highest power density at the expense of energy density. If the requirement is a huge power draw for a very short time (seconds), superca- pacitors may work well. Lead-acid bat- teries have the lowest power density. cycle life is the number of complete charge and discharge cycles an energy system can perform before it reaches 80% of its rated capacity. is characteristic is less important in backup solutions given that power outages are rare. Batteries are typically designed for 10 cycles a year. Su- percapacitors have the biggest cycle life (over 100,000 cycles). Lead-acid batteries have the lowest—fewer than 500 cycles. calendar life is the number of years for which the batteries have a recoverable capacity greater than 80%. It's a critical factor, as it determines how oen batteries must be replaced over the life of a server. Oen, the batteries in server rooms experience high temperatures, which age them much faster than room temperature. Supercapacitors have the best calendar life and can last for more than 10 years at elevated temperatures. Lithium-ion batteries can last up to 10 years with a lower charge voltage. Lead-acid bat- teries have the worst performance and may need replacement every two to four years. recharge time is the time required to charge from empty to full. It's a critical feature in a backup solu- tion, especially if back-to-back power outages are possible. e batteries must be fully charged as quickly as