Проверяем статус кеша:

megacli -LDInfo -LAll -a0

Получаем:

Virtual Drive: 1 (Target Id: 1)
Name                :
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 2.728 TB
Sector Size         : 512
Is VD emulated      : Yes
Mirror Data         : 2.728 TB
State               : Degraded
Strip Size          : 256 KB
Number Of Drives    : 2
Span Depth          : 1
Default Cache Policy: WriteThrough, ReadAhead, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteThrough, 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
Bad Blocks Exist: No
Is VD Cached: No

Включаем принудительно кэш на горячую:

megacli -LDSetProp EnDskCache -L0:0 -aAll

Set Disk Cache Policy to Enabled on Adapter 0, VD 0 (target id: 0) success
Set Disk Cache Policy to Enabled on Adapter 0, VD 0 (target id: 0) success

В итоге получаем:

Virtual Drive: 1 (Target Id: 1)
Name                :
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 2.728 TB
Sector Size         : 512
Is VD emulated      : Yes
Mirror Data         : 2.728 TB
State               : Degraded
Strip Size          : 256 KB
Number Of Drives    : 2
Span Depth          : 1
Default Cache Policy: WriteThrough, ReadAhead, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteThrough, ReadAhead, Direct, No Write Cache if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy   : Enabled
Encryption Type     : None
Bad Blocks Exist: No
Is VD Cached: No