Enabling and Disabling the Unit Write Cache

Write cache is used to store data locally in memory on the controller before it is written to the disk drive media, allowing the computer to continue with its next task. This improves performance. However, there may be instances when you 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.


	Note: If write cache is enabled, in the event of a power failure, the data in the controller cache will be lost if you do not have a Battery Backup Unit (BBU). To avoid a sudden power failure if you do not have a BBU, it is advisable to have an Uninterruptible Power Supply (UPS).

Write cache can be turned on or off for individual units in 3DM2, CLI, 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 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.


	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.

To enable or disable unit write cache through 3DM2

1	Choose Management >> Controller Settings from the menu bar in 3DM2.

2	In the Unit Policies section of the Controller Settings page, check the Write Cache box to enable it for the designated unit.

Show Write Cache Policy in 3DM2

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.

Related Topics: Working with Read Cache Settings; Enabling or Disabling Auto-Verify for a Unit; Setting Overwrite ECC (Continue on Source Error When Rebuilding); Enabling and Disabling Queuing for a Unit; Setting the StorSave Profile for a Unit; Rapid RAID Recovery