Monitor Write-through Caching Mode

The disk controller on each Exadata Storage Server periodically performs a discharge and charge of the controller battery. During the operation, the write cache policy changes from write-back caching to write-through caching. Write-through cache mode is slower than write-back cache mode. However, write-back cache mode has a risk of data loss if the Exadata Storage Server loses power or fails. For Exadata Storage Server releases earlier than release 11.2.1.3, the operation occurs every month. For Oracle Exadata Storage Server Software release 11.2.1.3 and later, the operation occurs every three months, for example, at 01:00 on the 17th day of January, April, July and October.

1. To change the start time for when the learn cycle occurs, use a command similar to the following. The time reverts to the default learn cycle time after the cycle completes.

   CellCLI> ALTER CELL bbuLearnCycleTime="2011-01-22T02:00:00-08:00"
   

2. To see the time for the next learn cycle, use the following command:

   CellCLI> LIST CELL ATTRIBUTES bbuLearnCycleTime
   

   The Exadata Storage Server generates an informational alert about the status of the caching mode for logical drives on the cell, for example:

   HDD disk controller battery on disk contoller at adapter 0 is going into a learn cycle. This is a normal maintenance activity that occurs quarterly and runs for approximately 1 to 12 hours. The disk controller cache might go into WriteThrough caching mode during the learn cycle. Disk write throughput might be temporarily lower during this time. The message is informational only, no action is required.
   

3. Use the following command to view the status of the battery:

   # /opt/MegaRAID/MegaCli/MegaCli64 -AdpBbuCmd -GetBbuStatus -a0
   

   The following is an example of the output of the command:

   BBU status for Adapter: 0
    
   BatteryType: iBBU08
   Voltage: 3721 mV
   Current: 541 mA
   Temperature: 43 C
    
   BBU Firmware Status:
    
   Charging Status : Charging
   Voltage : OK
   Temperature : OK
   Learn Cycle Requested : No
   Learn Cycle Active : No
   Learn Cycle Status : OK
   Learn Cycle Timeout : No
   I2c Errors Detected : No
   Battery Pack Missing : No
   Battery Replacement required : No
   Remaining Capacity Low : Yes
   Periodic Learn Required : No
   Transparent Learn : No
    
   Battery state:
    
   GasGuageStatus:
   Fully Discharged : No
   Fully Charged : No
   Discharging : No
   Initialized : No
   Remaining Time Alarm : Yes
   Remaining Capacity Alarm: No
   Discharge Terminated : No
   Over Temperature : No
   Charging Terminated : No
   Over Charged : No
    
   Relative State of Charge: 7 %
   Charger System State: 1
   Charger System Ctrl: 0
   Charging current: 541 mA
   Absolute State of Charge: 0%
    
   Max Error: 0 %
   Exit Code: 0x00