Avago Technologies MegaRAID SAS 9341-4i - Manual (Page 11)

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MegaRAID SAS Device Driver Installation User Guide
June 2015 Windows Driver Installation
MegaRAID Primary Storage
read performance. If your computer regularly performs random read requests, choose a smaller strip size. The
default is 64 KB.
— Access Policy: Select the type of data access that is allowed for this virtual drive.
RW: Permit read/write access. This setting is the default.
Read Only: Permit read-only access.
Blocked: Do not permit access.
— Read Policy: Specify the read policy for this virtual drive.
Normal: Disable the read-ahead capability. This setting is the default.
Ahead: Enable read-ahead capability, which permits the controller to read sequentially ahead of requested
data and to store the additional data in cache memory, anticipating that the data will be needed soon. This
setting speeds up read operations for sequential data, but little improvement exists when accessing random
data.
— Write Policy: Specify the write policy for this virtual drive.
WBack: In Write Back mode, the controller sends a data transfer completion signal to the host when the
controller cache has received all of the data in a transaction. This setting is recommended in Standard mode.
WThru: In Write Through mode, the controller sends a data transfer completion signal to the host when the
drive subsystem has received all of the data in a transaction. This setting is the default.
Write Back with BBU: Select this mode if you want the controller to use Write Back mode, but the controller
either has no battery backup unit (BBU) or the BBU is bad. If you do not choose this option, the controller
firmware automatically switches to Write Through mode if it detects a bad or missing BBU.
NOTE You can use Write Back mode with or without a battery. You should
use either a battery to protect the controller cache or an
uninterruptible power supply (UPS) to protect the entire system. If you
do not use a battery or a UPS, and a power failure occurs, you risk
losing the data in the controller cache. Although you can enable or
disable the disk cache, you should disable it. If you enable the disk
cache, the drive sends a data transfer completion signal to the
controller when the drive cache has received all the data in a
transaction. However, the data has not been actually transferred to the