ISS Technology Update, Volume 8, Number 2

ISS Technology Update Volume 8, Number 2

Expected life of the HP Smart Array BBWC upgrade module battery pack

The Smart Array 128-MB Battery-Backed Write Cache (BBWC) upgrade module uses a nickel metal hydride (NiMH) battery

pack to retain write data if power to the system is interrupted. Two important battery pack characteristics are its charge

capacity and battery life. Charge capacity, expressed in milliampere-hours (mAh), determines how long—in days—the BBWC

module can retain data. A new, fully-charged battery pack typically provides 5 to 6 days of data cache retention. However, the

data retention time decreases with higher operating temperature and increasing battery age. The battery pack is designed to

provide 3 days of data cache retention at 80 percent of its rated capacity. Data retention time is also affected by the size of the

cache. Therefore, larger caches (256 MB and 512 MB) include up to three battery modules to retain data up to 3 days.

Note

The data retention time can be extended any time the server's auxiliary power is available during system power down.

As the battery pack ages, the battery capacity decreases in a roughly linear manner (Figure 1-1). Battery aging is accelerated

by high server internal temperatures. In a worst case scenario with the sever operating at its maximum temperature of 60°C

(140°F), the battery pack has a life expectancy of 3 years, after which it should to be replaced. If the server‘s inlet temperature

is maintained at 24°C (75°F) or less, then the server‘s internal temperature should remain below 60°C, and the battery pack

may last more than three years. However, HP recommends replacing the battery pack every 3 years.

Figure 1-1. The Smart Array BBWC upgrade module is designed to provide 3 days of data retention at about 80 percent of its rated

capacity. Normally, the battery pack can last for more than 3 years. However, high system temperature accelerates aging and decreases

battery life.

Additional resources

For additional information on the topics discussed in this article, visit the following websites:

Resource

URL

HP Smart Array E200 Controller User Guide

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual

/c00688683/c00688683.pdf

HP Smart Array 6i Controller User Guide

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual

/c00217854/c00217854.pdf