Avago Technologies 3ware 9650SE-12ML (Channel) - Manual (Page 131)

Setting Unit Policies
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If you have a BBU (Battery Backup Unit) installed on the controller, the
battery preserves the contents of the controller cache memory for a limited
period of time (up to 72 hours) in the event of a system power loss. When a
BBU is installed, if the battery is not “Ready,” write cache is disabled and
cannot be enabled.
The unit's StorSave profile can also determine whether the write cache can be
enabled or disabled. A warning message will be given if the change is not
permitted due to the StorSave setting and the state of the unit.
To enable or disable unit write cache through 3DM
1 Choose Management > Controller Settings from the menu bar in 3DM.
2 In the Unit Policies section of the Controller Settings page, check the
Write Cache box to enable it for the designated unit.
The page refreshes, and a message at the top confirms the change you
have made.
If your system has no BBU, a message will caution you about enabling
write cache.
To enable or disable unit write cache through 3BM
1 At the main 3BM screen, select the unit by highlighting it and pressing
Enter.
An asterisk appears in the left-most column to indicate that it is selected.
2 Tab to the Maintain Unit button and press Enter .
3 On the pop-up menu, select Configure and press Enter .
4 In the Configure Disk Array screen, Tab to the field Write Cache
Settings .
Note: If the Write Cache checkbox is disabled (not selectable), check to see if the
unit has degraded or if the BBU is not ready. If a unit has a StorSave policy of
“Protect” and the unit degrades, the policy prevents write cache from being re-
enabled until the unit has been rebuilt or until the BBU is ready to use.