3Ware 9550SXU16MLB10 User Guide - Page 101

Enabling and Disabling the Unit Write Cache 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. For more information, see "Disabling Write Cache on Unit Degrade" on page 79. Write cache settings are not applicable for an unconfigured disk (JBOD). Note: Do not use Windows Control Panel to enable or disable cache on 3ware RAID units. Enabling and Disabling the Unit Write Cache through 3DM 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. www.3ware.com 95