Lenovo ThinkServer RD230, Software User'S Manual

Page: 93 / 364

Creating a Storage Configuration 4-17
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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.
Caution: Lenovo allows Writeback mode to be used with or without a
either
protect the controller cache, or an uninterruptible power
battery. It is recommended that you use
a battery to