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Enabling and Disabling the Unit Write Cache

Write cache is used to store data locally on the drive before it is written to the disk, allowing the computer to continue with its next task. Enabling write cache results in the most efficient access times for your computer system. However, there may be instances when you always want the computer to wait for the drive to write all the data to disk before going on to its next task. In this case, you must disable the write cache.

Write cache can be turned on or off for individual units in both 3DM and 3BM without changing the configuration or losing data from the drives.

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.

Notes:
For 9000-series controllers, a setting at the BIOS level in 3BM can specify that the cache should be disabled in the event the unit degrades. When that option is selected, unit write cache cannot be enabled until the array is rebuilt and again in optimal mode. In 3DM, you can see whether Disable write cache on unit degrade is set in the Other Controller Settings section of the Controller Settings page.

Write cache settings are not applicable for an unconfigured disk (JBOD).

To enable or disable unit write cache

  1. Choose Management > Controller Settings from the menu bar.
  2. In the Unit Write Cache section of the Controller Settings Page, select the Enabled or Disabled option for each unit.
  3. The page refreshes, and a message at the top confirms the change you have made.

For more information about the write cache settings, see the reference section, Controller Settings Page.


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