Avago Technologies MegaRAID SAS 9240-4i - Manual (Page 10)

LSI Corporation
- 10 -
MegaRAID SAS Device Driver Installation User Guide
December 2012
Chapter 2: Windows Driver Installation
MegaRAID Primary Storage
— 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 reads for sequential data, but little improvement exists 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 setting is the default.
Write Back with BBU: Select this mode if you want the controller to use Writeback 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 Writethrough mode if it detects a bad or missing BBU.
— IO Policy: The IO policy applies to reads on a specific virtual drive. It does not affect the read-ahead cache.
Direct: 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 setting is the default.
Cached: Reads are buffered in cache memory before they are sent to the host.
— 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 setting is the default.
— Disable BGI: Specify the background initialization status.
No: Leave background initialization enabled. A new configuration can be initialized in the background while
you use WebBIOS to perform other configuration tasks. This setting 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 or drives in MB, GB, or TB. Usually, this size is the full size for
RAID 1 shown in the Configuration panel on the right. You may specify a smaller size if you want to create
other virtual drives on the same drive group.
— Update Size: Click Update Size to update the Select size field value for the selected RAID levels.
16. Either click Accept to accept the changes to the virtual drive definition, or click Reclaim to return to the
previous settings.
17. Click Next after you finish defining virtual drives.
The Configuration Preview window appears.
18. Check the information in the configuration preview.
19. If the virtual drive configuration is acceptable, click Accept to save the configuration. Otherwise, click Back to
return to the previous screens and change the configuration.
20. If you accept the configuration, click Yes at the prompt to save the configuration and initialize the new
virtual drive.
NOTE You can use Writeback 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
disk media, so you risk losing the data in the disk cache if a power failure occurs. The data
is unrecoverable.