Understanding HP Smart Array

HP Array cards which have no BBWC only support Raid 0 and 1.

If you add a BBWC(Battery-backed write cache) it add extra memory to the cache and provides battery backup so if you lose power to the server. The data is saved in the cache which had not been written to the disk at the time of the power failure . When the power is restored to the server the raid controller continues where it left off and writes the data to the disk.

Adding a BBWC improves the performance of the raid via Array Accelerator and also provides:

  • Online RAID level migration
  • Online stripe size migration
  • Online array expansion
  • Online logical drive extension
  • Online drive firmware upgrade

To Check if you have a BBWC installed  run the following comand:

ctrl slot=1 show

Smart Array P400 in Slot 1
Bus Interface: PCI
Slot: 1
Serial Number:
Cache Serial Number:
RAID 6 (ADG) Status: Enabled
Controller Status: OK
Hardware Revision: Rev D
Firmware Version: 7.08
Rebuild Priority: Medium
Expand Priority: Medium
Surface Scan Delay: 15 secs
Surface Scan Mode: Idle
Wait for Cache Room: Disabled
Surface Analysis Inconsistency Notification: Disabled
Post Prompt Timeout: 0 secs
Cache Board Present: True
Cache Status: OK
Accelerator Ratio: 25% Read / 75% Write
Drive Write Cache: Disabled
Total Cache Size: 512 MB
No-Battery Write Cache: Disabled
Cache Backup Power Source: Batteries
Battery/Capacitor Count: 1
Battery/Capacitor Status: OK
SATA NCQ Supported: True

You can see the text in red show it has a Battery and Cache module installed and the Accelerator Ratio.

Also to see the Array Accelerator is enable on the Logiacl drive run the following command:

ctrl slot=1 ld 1 show detail

Smart Array P400 in Slot 1

array A

Logical Drive: 1
Size: 136.7 GB
Fault Tolerance: RAID 1
Heads: 255
Sectors Per Track: 32
Cylinders: 35132
Strip Size: 128 KB
Status: OK
Array Accelerator: Enabled

To do any task which you require a BBWC, make sure you have a battery present and is fully charged if you not you can not perform any of these task.

You may also notice that two options are  Drive Write Cache: and No-Battery Write Cache which are disabled. The following describes them:

Drive Write Cache: If enable means the array will use the onboard cache on the hard drive. It will write the data here first and then to the disk. If the server is not procted via UPS and looses power. Data in the cache will be lost and cause data corruption on the hard drive.

No-Battery Write Cache:If you have no battery installed or it is failed you can enable this feature to use the on-board cache of the raid controller.But if  the server is not protected via UPS and looses power. Data in the cache will be lost and cause data corruption on the hard drive.

There is a good article which describe this better:http://www.tricksguide.com/how-to-expand-array-extend-logical-drive-raid-hp-acu.html


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