Dell PowerEdge RAID Controller H800 - Manual (Page 37)

Storage Controller Features 37
Cache Preservation With Battery
The lithium-ion battery included in the BBU/TBBU of the controller is an
inexpensive way to protect data in cache memory. If the controller has data in
cache memory during a power outage or improper system shutdown, battery
power is used to preserve cache data until power is restored or the battery is
depleted. Under the 1-year limited warranty, the battery provides at least 24
hours of backup power coverage in normal operating conditions during the
warranty period. To prolong battery life, do not store or operate the battery in
temperatures that exceed 60 degrees C.
Cache Preservation With Non-Volatile Cache (NVC)
The NVC module allows controller cache data to be stored indefinitely, an
advantage over the 24 hours that battery backup provides. If the controller
has data in cache memory during a power outage or improper system
shutdown, a small amount of power from a battery is used to transfer cache
data to non-volatile flash storage where it remains until power is restored and
the system is booted.
Cache Data Recovery
The dirty cache LED that is located on the H700 and H800 cards cannot be
used to determine if cache data is being preserved. If a system power loss or
improper system shutdown has occurred, restore system power and boot the
system. During the boot, enter the controller's BIOS Configuration Utility
(<Ctrl><R>) to ensure that there is no cache data being preserved. This
can be done by entering into the controller menu and selecting Managed
Preserved Cache. If there are no virtual disks listed here, all preserved cache
data has been written to disk successfully.
In the event of a PERC H800 card failure, the entire TBBU/TNVC module
can be safely transferred to a new PERC H800 card without putting preserved
cache data at risk. See the applicable sections in "Installing and Configuring
Hardware" on page 41 for instructions on removing and installing the
TBBU/TNVC, then follow the instructions above on recovering cache data.
PERC7.2_UG.book Page 37 Thursday, March 3, 2011 2:14 PM