Monitoring Hard Disk Controller Write-Through Cache Mode

The hard disk controller on each 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 risks data loss if the storage server loses power or fails. The operation occurs every three months, for example, at 01:00 on the 17th day of January, April, July and October.

This example shows an informational alert that a storage server generates about the status of the caching mode for its logical drives:

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.

Use the following commands to manage changes to the periodical write cache policy:

To change the start time for the learn cycle, use a command like the following example:
```
CellCLI> ALTER CELL bbuLearnCycleTime="2013-01-22T02:00:00-08:00"
```
The time reverts to the default learn cycle time after the cycle completes.

To see the time for the next learn cycle:

CellCLI> LIST CELL ATTRIBUTES bbuLearnCycleTime

To view the status of the battery:

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

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