Enabling and Disabling the Unit Write Cache

Write cache is used to store data locally in memory on the drive before it is written to the disk drive media, 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.

For 9550SX and 9590SE controllers, when write cache is enabled, a StorSave profile specifies the level of data protection that you want for this unit. For more information, see Setting the StorSave Profile for a Unit.

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.

Notes:
For 9500S 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 unit 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 9550SX and 9590SE controllers, the Disable write cache on unit degrade setting is part of the StorSave Profile.

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

If the StorSave Profile is "protect" and a unit has degraded, write cache can- not be enabled.

Do not use Windows Control Panel to enable or disable cache on 3ware RAID units.

To enable or disable unit write cache

Choose Management > Controller Settings from the menu bar in 3DM.

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.