Inspur 3408 Series Configuration Manual page 35

Parameter
Read Policy
Write Policy
I/O Policy
Description
Read policy of virtual drives, including:
No Read Ahead: Read Ahead disabled.

Read Ahead: Read Ahead enabled. The controller can

read sequential data ahead or predict data to be used
and cache it.
Write policy of virtual drives.
Write Back: When the controller has no BBU (Battery

Backup Unit), the BBU is charging/discharging or
damaged, or the pinned/preserved cache reaches 50%
of the physical cache capacity of the RAID controller
card, the RAID controller card automatically switches to
the Write Through mode. This mode is the
recommended standard mode.
Write Through: After the disk subsystem receives all

data transmitted, the controller returns a data
transmission completion signal to the server.
Always Write Back: After the cache of the controller

receives all data transmitted, the controller returns a
data transmission completion signal to the server.
Note:
In Always Write Back mode, if super-capacitor is absent or
in the charging state, the written data in DDR memory of the
RAID controller card will be lost. This mode is not
recommended.
I/O policy of virtual drives for specific virtual drive read
scenarios, which does not affect cache of Read Ahead. Only
the Direct mode is available to 94xx series or later controller
cards.
Direct: In read scenarios, data is directly read from

drives. (except for the case where Read Policy is set to
Read Ahead, in which case read data is cached on the
RAID controller card.)
In write scenarios, written data is cached on the RAID

controller card. (except for the case where Write Policy is
set to Write Through, in which case data is directly
written into drives without being cached on the RAID
controller card.)
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