Avago Technologies MegaRAID Fast Path Software - Manual (Page 76)

Page 76 LSI Corporation Confidential | July 2011
MegaRAID SAS Software User Guide Chapter 4: WebBIOS Configuration Utility | Creating a Storage Configuration
— Read Policy: Specify the read policy for this virtual drive
Normal: This option disables the read ahead capability. This option is the default
setting.
Ahead: This option 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 option
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 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 is the default setting.
Write Back with BBU: Select this mode if you want the controller to use Write
back 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 Write through
mode if it detects a bad or missing BBU.
CAUTION: LSI allows Write back mode to be used with or without a BBU. LSI
recommends that you use either a battery to protect the controller cache, or an 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.
— 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 option is the default setting.
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. This option is the default setting.
NoChange: Leave the current drive cache policy as is.
— Disable BGI: Specify the Background Initialization (BGI) status:
No: Leave background initialization enabled, which 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 drives in MB, GB, or TB. Usually, this
would be the full size for RAID 1 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.