4-9
Chapter 4: MegaRAID BIOS Configuration Utility
• When the disk Write Cache is ON, a write transaction is considered to be complete
when all the data has been written to the disk cache. When disk Write Cache is OFF,
the write transaction is complete only when the data has been written to the disk.
• When disk Read Ahead is ON, extra data is read sequentially ahead of the data that
is actually requested and is stored in a cache. If the additional read-ahead data is
then requested, it can be read faster from the cache than from the disk directly.
Follow these steps to view or change the virtual drive Write Cache or Read Ahead
settings:
1. From the MANAGEMENT menu, select OBJECTS J VIRTUAL DRIVE J VIRTUAL DRIVE N
J VIEW/UPDATE PARAMETERS.
2. Use the arrow key to move the cursor to DISK WC or READ AHEAD and press ENTER.
3. Use the arrow key to select OFF or ON for DISK WC (DWC) or READ AHEAD.
4. When you see the prompt, CHANGE DWC or CHANGE READ AHEAD, use the arrow
key to select OFF or ON, then press ENTER to change the cache setting.
The settings are changed for all virtual drives defined on the array.
4-4 Rebuilding a Drive
The MegaRAID BIOS CU enables you to rebuild a drive of a redundant array if the array
has a failed drive. If the failed drive is still good (that is, if the drive is physically present
and its size is greater than or equal to the defined size of the array) it will be rebuilt. If the
drive is small, an error message will appear and the MegaRAID BIOS CU will not allow
the drive to be rebuilt. A rebuild cannot be started on a failed drive if its size is even 1
byte smaller than the defined size of the array.
Rebuilding a Drive
Follow these steps to rebuild a drive:
1. Select REBUILD from the MANAGEMENT menu.
2. When the list of drives appears, highlight the FAIL drive that you want to rebuild and
press the SPACEBAR to select it.
3. After selecting the physical drive, press F10 and select YES at the confirmation
prompt.
The rebuild process begins, and a graph shows the progress of the rebuild until it is
complete. Although the CU changes the disk drive state to REBUILD at this point, the
change does not appear on the screen while the rebuild is in progress.
When rebuild is complete, the CU displays the message:
NOTE: When the disk Write Cache is ON, there is a danger that data could be
lost if the power fails before the cached data is written to disk.