HP Smart Array Controller technology, 4th edition

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auxiliary power if available. An amber LED on the cache module or battery pack begins flashing to indicate
that data is in the cache. Smart Array controllers automatically write this data to disk when the system
powers up. The posted-write data in the cache will be lost if the batteries drain completely before the system
powers up. The batteries automatically recharge when the system has power. Battery recharge takes
between 30 minutes and 2 hours, depending on the remaining capacity level.
If the server fails, you can move the Smart Array controller and all of the drives to another server to allow
writing the data in the cache to the drives.
If the controller fails, you can move the cache module containing posted-write data to a new Smart Array
controller. You must attach the new Smart Array controller to the original drives to preserve cache data.
You should be aware of a special concern when using an embedded RAID controller with battery-backed
cache. If the server board fails, the replacement board must be the same model server board. The controller
type and drive bays must be the same. The cache module, battery pack, and drives move to the
replacement system to extract the data from the battery-backed cache.
HP selection criteria f
or battery-backed cache
We designed the Smart Array battery cells, battery enclosures, and contacts to preserve the integrity of your
data beyond the minimum specified backup duration. Battery life is about three years in typical server
environments.
A dedicated battery microcontroller continuously monitors the HP Smart Array battery pack for signs of
damage, including an open battery terminal, partial battery short, charge timeouts, and over discharge
conditions. You can see the battery status with:
 LED
 Power-on self-test (POST) messages
 Event messages to the host
 ACU information pages
 Array Diagnostic Utility (ADU)
 HP SIM
The battery microcontroller automatically disables the battery-backed cache features any time it detects
battery damage or the charge level falls below the required limits to achieve the specified backup duration.
The battery microcontroller automatically restores battery-backed cache features when the microcontroller
detects a replacement battery or when battery recharging is complete. High-end HP Smart Array controllers
contain two batteries to protect against a single battery cell failure.
Types of batteries
HP Smart Array controll
ers use rechargeable Nickel Metal Hydride (NiMH) button cell batteries specifically
designed for long life at server temperatures. The HP 650 mAh P-Series battery has the same form factor as
previous versions and extends battery life up to 48 hours before you need to recharge it. Typical capacity
for the HP Smart Array battery pack reduces by 5 to 10 percent over a 3-year period, depending on server
temperature and number of discharge cycles.
NiMH cells do not contain harmful lead, mercury, or cadmium material. Additionally, NiMH chemistry does
not suffer capacity memory effects that can lower battery capacity. For example, short discharge cycles
reduce the memory capacity of Nickel Cadmium (NiCd) batteries. Lithium Ion (Li-Ion) batteries are typically
smaller than NiMH batteries, but their capacity is permanently reduced at high temperatures and they are
usually limited to 100 full discharge cycles.
Battery replacement
HP Smart Array controll
ers include serviceable battery packs that allow tool-free battery pack replacement
with no need to replace either the Smart Array controller or the detachable cache module.