引言
MegaCli是一个非常有用的工具，无论是创建raid、获取raid信息还是修改raid设置。本文focus在BBU和write policy以及disk cache policy信息的获取和修改。
是否存在BBU
如何查看是否存在BBU：
/opt/MegaRAID/MegaCli/MegaCli64 -AdpBbuCmd -aAll
当没有BBU时，输出如下：
root@yb-test:/opt/MegaRAID/MegaCli# ./MegaCli64 -AdpBbuCmd -aAll
Adapter 0: Get BBU Status Failed.
FW error description:
The required hardware component is not present.
Exit Code: 0x22
BBU的相关信息
如果系统存在BBU的话，输出的信息如下：
root@node-2:/opt/MegaRAID/MegaCli# ./MegaCli64 -AdpBbuCmd -Aall
BBU status for Adapter: 0
BatteryType: iBBU-09
Voltage: 3996 mV
Current: 0 mA
Temperature: 53 C
**Battery State: Optimal**
Design Mode : 48+ Hrs retention with a non-transparent learn cycle and moderate service life.
BBU Firmware Status:
Charging Status : None
Voltage : OK
Temperature : OK
Learn Cycle Requested : Yes
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 : No
Periodic Learn Required : No
Transparent Learn : No
No space to cache offload : No
Pack is about to fail & should be replaced : No
Cache Offload premium feature required : No
Module microcode update required : No
BBU GasGauge Status: 0x0180
Relative State of Charge: 89 %
Charger System State: 1
Charger System Ctrl: 0
Charging current: 0 mA
Absolute state of charge: 77 %
Max Error: 0 %
Battery backup charge time : 48 hours +
BBU Capacity Info for Adapter: 0
Relative State of Charge: 89 %
Absolute State of charge: 77 %
Remaining Capacity: 1169 mAh
Full Charge Capacity: 1324 mAh
Run time to empty: Battery is not being charged.
Average time to empty: 2 Hour, 20 Min.
Estimated Time to full recharge: Battery is not being charged.
Cycle Count: 3
BBU Design Info for Adapter: 0
Date of Manufacture: 09/03, 2013
Design Capacity: 1500 mAh
Design Voltage: 4100 mV
Specification Info: 0
Serial Number: 7968
Pack Stat Configuration: 0x0000
Manufacture Name: LS36691
Firmware Version :
Device Name: iBBU-09
Device Chemistry: LION
Battery FRU: N/A
Transparent Learn = 0
App Data = 0
BBU Properties for Adapter: 0
Auto Learn Period: 28 Days
Next Learn time: Thu Mar 31 15:16:22 2016
Learn Delay Interval:0 Hours
Auto-Learn Mode: Enabled
BBU Mode = 5
Exit Code: 0x00
其中加粗的信息Optimal表示BBU状态正常。
BBU是由锂离子电池和电子控制电路组成，电池的寿命取决于其老化程度，无论是否充放电已经充放电的多少，锂离子电池的容量都会减少。为了记录电池的放电曲线，延长电池的寿命，默认会启用自动校准模式（AutoLearn Mode），在Learn Cycle 内，Raid卡控制器不会使用BBU，这个过程可能持续12小时，这个过程中会禁用Write back，直到其完成校准。
这个Auto-Learn Mode，一般30天执行一次，我们的BBU 28天之星一次。一般不要关闭，因为这可以有效地延长寿命。如果不做这个校准，寿命会从2年下降到8个月。
充电过程中，BBU相关的信息如下：
root@yb-test:/opt/MegaRAID/MegaCli# ./MegaCli64 -AdpBbucmd -aAll
BBU status for Adapter: 0
BatteryType: iBBU-09
Voltage: 3955 mV
Current: 527 mA
Temperature: 36 C
**Battery State: Degraded(Charging)**
Design Mode : 48+ Hrs retention with a non-transparent learn cycle and moderate service life.
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
No space to cache offload : No
Pack is about to fail & should be replaced : No
Cache Offload premium feature required : No
Module microcode update required : No
BBU GasGauge Status: 0x0100
Relative State of Charge: 63 %
Charger System State: 1
Charger System Ctrl: 0
Charging current: 527 mA
Absolute state of charge: 52 %
Max Error: 0 %
Battery backup charge time : 42 hours
...
Exit Code: 0x00
BBU相关的cache policy
通过执行 MegaCli64 -LDIno -Lall -aALL可以查看默认的cache policy，
/opt/MegaRAID/MegaCli/MegaCli64 -LDInfo -Lall -aALL
Default Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
其中No Write Cache if Bad BBU表示BBU有问题的时候，禁用write cache，这种做法是安全负责任的。
另外一种不负责任的选项是 Write Cache OK if Bad BBU。分别可以采用以下命令修改：
/opt/MegaRAID/MegaCli/MegaCli64 -LDSetProp CachedBadBBU -Lall -aALL
root@node-2:/opt/MegaRAID/MegaCli# ./MegaCli64 -LDSetProp CachedBadBBU -Lall -aALL
Set Write Cache OK if bad BBU on Adapter 0, VD 0 (target id: 0) success
Set Write Cache OK if bad BBU on Adapter 0, VD 1 (target id: 1) success
Set Write Cache OK if bad BBU on Adapter 0, VD 2 (target id: 2) success
Set Write Cache OK if bad BBU on Adapter 0, VD 3 (target id: 3) success
Set Write Cache OK if bad BBU on Adapter 0, VD 4 (target id: 4) success
改过之后，可以查看，变成了Write Cache OK if Bad BBU
Virtual Drive: 2 (Target Id: 2)
Name :
RAID Level : Primary-0, Secondary-0, RAID Level Qualifier-0
Size : 7.275 TB
Sector Size : 512
Is VD emulated : No
Parity Size : 0
State : Optimal
Strip Size : 128 KB
Number Of Drives : 4
Span Depth : 1
Default Cache Policy: WriteBack, ReadAhead, Direct, Write Cache OK if Bad BBU
Current Cache Policy: WriteBack, ReadAhead, Direct, Write Cache OK if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy : Disk's Default
Encryption Type : None
PI type: No PI
Is VD Cached: No
当然了这种策略是不负责任的，我们需要改成No Write Cache if Bad BBU，方法如下：
/opt/MegaRAID/MegaCli/MegaCli64 -LDSetProp -NoCachedBadBBU -Immediate -Lall -aAll
输出情况及查看是否生效：
root@node-2:/opt/MegaRAID/MegaCli# ./MegaCli64 -LDSetProp -NoCachedBadBBU -Lall -aAll
Set No Write Cache if bad BBU on Adapter 0, VD 0 (target id: 0) success
Set No Write Cache if bad BBU on Adapter 0, VD 1 (target id: 1) success
Set No Write Cache if bad BBU on Adapter 0, VD 2 (target id: 2) success
Set No Write Cache if bad BBU on Adapter 0, VD 3 (target id: 3) success
Set No Write Cache if bad BBU on Adapter 0, VD 4 (target id: 4) success
Exit Code: 0x00
Virtual Drive: 2 (Target Id: 2)
Name :
RAID Level : Primary-0, Secondary-0, RAID Level Qualifier-0
Size : 7.275 TB
Sector Size : 512
Is VD emulated : No
Parity Size : 0
State : Optimal
Strip Size : 128 KB
Number Of : 4
Span Depth : 1
Default Cache Policy: WriteBack, ReadAhead, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAhead, Direct, No Write Cache if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy : Disk's Default
Encryption Type : None
PI type: No PI
Is VD Cached: No
disk cache policy
按照最佳设置，这个disk cache policy应该关闭，
关闭的命令上一篇博文有提到，
关闭disk cache
/opt/MegaRAID/MegaCli/MegaCli64 -LDSetProp -DisDskCache -Immediate -Lall -aAll
开启disk cache
/opt/MegaRAID/MegaCli/MegaCli64 -LDSetProp -EnDskCache -Immediate -Lall -aAll