Lenovo ThinkServer RD240 MegaRAID SAS Software User Guide - Page 98

performance. If your computer regularly performs random read requests, choose a smaller stripe size. The default is 64 Kbytes. • Access Policy: Select the type of data access that is allowed for this virtual drive: ◊ RW: Allow read/write access. This is the default. ◊ Read Only: Allow read-only access. ◊ Blocked: Do not allow access. • Read Policy: Specify the read policy for this virtual drive: ◊ Normal: This disables the read ahead capability. This is the default. ◊ Ahead: This enables read ahead capability, which allows 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 speeds up reads for sequential data, but there is little improvement when accessing random data. ◊ Adaptive: When Adaptive read ahead is selected, the controller begins using read ahead if the two most recent drive accesses occurred in sequential sectors. If the read requests are random, the controller reverts to Normal (no read ahead). • Write Policy: Specify the write policy for this virtual drive: ◊ WBack: In Writeback 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 Writethrough 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 is the default. ◊ Bad BBU: Select this mode if you want the controller to use Writeback mode but the controller has no BBU or the BBU is bad. If you do not choose this option, the controller firmware automatically switches to Writethrough mode if it detects a bad or missing BBU. 4-22 WebBIOS Configuration Utility