How to activate write cache on P400 Smart Controller

[kjcsb]

I have a DL320 G5 with a P400 controller. I've recently installed a battery-backed write cache.

hpacucli controller slot=2 show

Smart Array P400 in Slot 2
Bus Interface: PCI
Slot: 2
Serial Number: PAFGL0R9SX81HJ
Cache Serial Number: PA82C0J9SX90QL
RAID 6 (ADG) Status: Enabled
Controller Status: OK
Chassis Slot:
Hardware Revision: Rev E
Firmware Version: 5.22
Post Prompt Timeout: 0 secs
Cache Board Present: True
Cache Status: Not Configured
Drive Write Cache: Disabled
Total Cache Size: 256 MB
No-Battery Write Cache: Disabled
Cache Backup Power Source: Batteries
Battery/Capacitor Count: 1
Battery/Capacitor Status: OK
SATA NCQ Supported: True

How can I enable the drive write cache?

hpacucli controller slot=2 modify dwc=enable
Warning: Without the proper safety precautions, use of write cache on physical drives could cause data loss in the event of power failure. To ensure data is properly protected, use redundant power supplies and Uninterruptible Power Supplies. Also, if you have multiple storage enclosures, all data should be mirrored across them. Use of this feature is not recommended unless these precautions are followed.
Continue? (y/n) y


Error: This operation is not supported with the current configuration. Use the "show" command on devices to show additional details about the configuration.

hpacucli controller slot=2 modify nobatterywritecache=enable
Error: This operation is not supported with the current configuration. Use the "show" command on devices to show additional details about the configuration.

P.S. this thread has been moved from Storage > General to ProLiant Servers (ML,DL,SL) - Hp Forum Moderator

[Uwe Zessin]

The BBWC in the controller ***DOES NOT*** protect the disk drive's cache memory !!!!!

That can only be done by a UPS external to the server and even then *I* would not enable DWC.

[kjcsb]

Thanks
"The BBWC in the controller ***DOES NOT*** protect the disk drive's cache memory !!!!!"

What does the BBWC do then?

"That can only be done by a UPS external to the server and even then *I* would not enable DWC."

The server is connected to a UPS. How do I enable the drive write cache?

[Uwe Zessin]

The BBWC does protect the cache memory within the controller module.

[kjcsb]

Thanks. Any suggestions on how to enable the drive write cache?

[Uwe Zessin]

I've never looked into this, sorry.

I beleive it is an error to enable it in a production environment. The risks are greatly increased, because a complete server (with its embedded drives) can much easier experience a power failure.

If the BBWC goes bad, the SmartArray controller goes into write-through mode. If somebody accidently turns off the server (or must do it because it has locked up) - the data in the DWC is gone!! There is NO way to notify the disk drives about an emergency to flush their cache!

[kris rombauts]

Hi,

i tried that command to enable the write cache on the hard disks and in my config it works (see output below). However , as already mentioned, it is not recommended to do this, this has nothing to do with the BBWC you just installed. When a server hang/crashes or power failure occurs, the data in the disk drives write cache (if present and not flushed yet) will be lost and you highly increase the risc for data corruption.

One thing i can think about is, maybe the BBWC battery is not fully charged yet when you took the CLI output and this is why the 'cache status' is still listed as "not configured" or you did not yet check the properties of your logical drives and enabled the write back cache there.


Output of the cli (on a Windows box) :


=> show detail

Smart Array P400 in Slot 4
Bus Interface: PCI
Slot: 4
Serial Number: xxxxxx
Cache Serial Number: xxxxx
RAID 6 (ADG) Status: Enabled
Controller Status: OK
Chassis Slot:
Hardware Revision: Rev D
Firmware Version: 5.20
Rebuild Priority: Low
Expand Priority: Low
Surface Scan Delay: 15 secs
Surface Analysis Inconsistency Notification: Disabled
Raid1 Write Buffering: 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: 256 MB
No-Battery Write Cache: Disabled
Cache Backup Power Source: Batteries
Battery/Capacitor Count: 1
Battery/Capacitor Status: OK
SATA NCQ Supported: True


=> modify dwc=enable

Warning: Without the proper safety precautions....... Use of this
feature is not recommended unless these precautions are followed.
Continue? (y/n) y

=> show detail

Smart Array P400 in Slot 4
Bus Interface: PCI
Slot: 4
Serial Number: P61620E9SV60LH
Cache Serial Number: PA82C0H9SV6C3S
RAID 6 (ADG) Status: Enabled
Controller Status: OK
Chassis Slot:
Hardware Revision: Rev D
Firmware Version: 5.20
Rebuild Priority: Low
Expand Priority: Low
Surface Scan Delay: 15 secs
Surface Analysis Inconsistency Notification: Disabled
Raid1 Write Buffering: Disabled
Post Prompt Timeout: 0 secs
Cache Board Present: True
Cache Status: OK
Accelerator Ratio: 25% Read / 75% Write
Drive Write Cache: Enabled <---
Total Cache Size: 256 MB
No-Battery Write Cache: Disabled
Cache Backup Power Source: Batteries
Battery/Capacitor Count: 1
Battery/Capacitor Status: OK
SATA NCQ Supported: True


HTH

Kris

[werenzo]

Hi,

I solved with that command

hpacucli controller slot=0 logicaldrive 1 modify arrayaccelerator=enable

In my server I have logicaldrive 1 running on slot 0

[Jamsnz]

Don't - its recommended configuration not to enable drive write cache on disk drives and leave write caching to the controller card cache.