Enabling Write back cache using hpacucli

Hi,

Write back cache enabled systems are mostly more optimized because writing into the cache is faster than writing into the disk. Lets look how can we enable this feature for the controller using hpacucli.

To Display :
hpacucli ctrl all show config detail

This command’s output is starting with :

Smart Array P400 in Slot 1
Bus Interface: PCI
Slot: 1  <<< This is the Slot# (We will use it to enable Write back cache)
Serial Number: PXXXXXXXXX
Cache Serial Number: PXXXXXXX
RAID 6 (ADG) Status: Enabled
Controller Status: OK
Chassis Slot:
...
Cache Board Present: True
Cache Status: OK
Accelerator Ratio: 25% Read / 75% Write
Drive Write Cache: Disabled <<< This Means Write back cache is disabled
Total Cache Size: 512 MB <<< This is the size of cache
No-Battery Write Cache: Disabled <<< This means when Battery is Not OK, WRB will be automatically get disabled.
Cache Backup Power Source: Batteries
Battery/Capacitor Count: 1 <<< One Battery is present
Battery/Capacitor Status: OK <<< Battery is OK
SATA NCQ Supported: True
....

To enable WBC please run this command :

ctrl slot=1 modify dwc=enable

When you run this command a warning message is shown about possible loss of data in the event of power failure.
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

If no problem with this message , you can pree y and go on.

That’s all.

Good luck 🙂  

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2 thoughts on “Enabling Write back cache using hpacucli

  1. You are confusing the controller cache (which is protected by the battery module) with cache on the disks itself (“Drive Write Cache” in hpacucli output), which is not protected by the battery module and in case of power failure the data in disk’s cache will be lost.

    Liked by 1 person

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