NEC Express 5800 User Manual page 362

Hardware
The Write Policy has the following modes depending on combination with WrtThru for BAD BBU.
Select a mode suitable for your environment.
Write Policy WBack
WThru
You can change parameters for VD definition except for RAID Level and Stripe Size. On the
WebBIOS Home Menu, select [Virtual Disks], press Enter, and specify parameters in "Policies"
frame, then select [Change] and press Enter.
WrtThru for BAD BBU
Checked
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.
Write through mode
The controller does not use
cache memory for writing
data.
This mode can provide
higher data security,
however, writing performance
is lower than that in WBack
mode.
362
Unchecked
Constant write back mode
The controller always uses
cache memory for writing. In
this mode, the data in cache
memory may not be protected
from being lost if the power
failure occurs due to
charge/discharge or defect of
the 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.