NEC Express5800/B120b User Manual page 121

The Write Policy has the following modes depending on combination with WrtThru for BAD BBU.
Select a mode suitable for your environment.
WrtThru for BAD BBU
Checked
Write WBack Normal write back mode
Policy
* There is no additional battery for
WThru Write through mode
The controller does not use cache
memory for writing data.
This mode can provide the highest
data security, however, the writing
performance is lower than that in
write back mode.
IMPORTANT:
If constant write back mode is selected, the controller operates in
write back mode even if the battery has failed, insufficiently charged,
or no battery has been installed. The data in cache memory may be
lost at an occurrence of power failure.
Be sure to use UPS when specifying the constant write back mode
for write policy.
the controller, so the controller
operates in write through mode.
Configuring Your Server 4-71
Unchecked
Constant write back mode
The controller always uses cache
memory for writing regardless of battery
charged status or existence of battery.
Be sure to use UPS when specifying
this mode for write policy.
* This mode is unavailable.
If you do not check "WrtThru for BAD
BBU" at creation of VD, this item is
automatically checked after the VD has
been created.