Lenovo ThinkServer RD330 Software User's Manual page 94

Chapter 4: WebBIOS Configuration Utility
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Creating a Storage Configuration
— 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.
— 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: We allow Writeback mode to be used with or without a battery. We
recommend that you use either a battery to protect the controller cache, or a UPS to
protect the entire system. If you do not use a battery or a UPS, and there is a power
failure, you risk losing the data in the controller cache.
— IO Policy: The IO Policy applies to reads on a specific virtual drive. It does not
affect the read ahead cache.
Direct: In Direct I/O mode, reads are not buffered in cache memory. Data is
transferred to the cache and the host concurrently. If the same data block is read
again, it comes from cache memory. This is the default.
Cached: In Cached I/O mode, all reads are buffered in cache memory.
— Drive Policy: Specify the drive cache policy:
Enable: Enable the drive cache.
Disable: Disable the drive cache.
NoChange: Leave the current drive cache policy as is. This drive policy is the
default.
— Disable BGI: Specify the background initialization status:
No: Leave background initialization enabled. This means that a new
configuration can be initialized in the background while you use WebBIOS to do
other configuration tasks. This is the default.
Yes: Select Yes if you do not want to allow background initializations for
configurations on this controller.
— Select Size: Specify the size of the virtual drive in megabytes. Normally, this
would be the full size for RAID 10 shown in the configuration panel on the right.
You can specify a smaller size if you want to create other virtual drives on the
same drive group.
MegaRAID SAS Software User Guide