User`s guide

Configuring Your Server 4-83
The Write Policy has the following modes depending on combination with WrtThru for BAD BBU. Select a mode suitable for
your environment.
WrtThru forBAD BBU
Checked Unchecked
Write
Policy
WBack
Normal write back mode
(recommended)
The controller uses cache memory
for writing. However, if the battery is
being charged or failed, the
controller operates in WThru (write
through) mode automatically. Thus,
this mode can provide higher data
security.
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.
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 the one in
write back mode.
* This mode is unavailable.
If you do not check "WrtThru for
BAD BBU" when creating a VD, this
item is automatically checked after
the VD has been created.
IMPORTANT:
 If the constant write back mode is selected, the controller operates in write back mode even if
the battery has failed or is insufficiently charged. The data in cache memory may be lost if a
power failure occurs.
 Be sure to use an UPS when specifying the constant write back mode as write policy.