# Understanding logical-drive synchronization

The purpose of synchronizing logical drives is to compute and write the parity data on the selected drives. Synchronizing a logical drive verifies that the data redundancy for the logical drive is correct.

Note: You can determine if your controller firmware supports auto-synchronization and data scrubbing by viewing the controller information pane. The information pane reports if these features are enabled or disabled.

## Using auto-synchronization

If the logical drive is attached to a controller that supports auto-synchronization, the ServeRAID Manager automatically synchronizes all new RAID level-5, 5E, and 50 logical drives. These logical drives must be synchronized before storing data. Auto-synchronization ensures that the parity data is accurately computed. Accurate parity is critical for updating the parity when you begin to store data.

You do not auto-synchronize RAID level-1, 1E, 10, and 1E0 logical drives because they do not use parity data.

During auto-synchronization, the ServeRAID Manager displays a progress indicator in the status bar. You can perform any other actions on the controller during an auto-synchronization. Also, you can turn off the server during an auto-synchronization and, when you turn on the server, the firmware will continue the auto-synchronization where it left off.

## Using manual synchronization

When you create a logical drive that is attached to a controller that does not support auto-synchronization, you will receive a warning event in the event viewer stating that you must manually synchronize the logical drive before storing data. Use "Synchronize logical drives" to manually synchronize the logical drive. You must synchronize new RAID level-5 logical drives after you create them.

Manual synchronization can be a lengthy operation. You cannot perform any other actions on the controller until the manual synchronization is completed. Do not turn off the server until the manual synchronization is complete. The ServeRAID Manager displays a progress indicator in the status bar.

## Using manual synchronization for data scrubbing

Data scrubbing is an automatic background synchronization process. Data scrubbing keeps data "fresh" by doing the following:

- (For RAID level-5, 5E, or 50) Reading data and rewriting the data parity.
- (For RAID level-1, 1E, 10, 1E0) Reading data and rewriting the mirror data.

If data scrubbing is disabled or your controller firmware does not support data scrubbing, consider manually synchronizing your logical drives weekly. This does not alter data on the drive.

Note: If data scrubbing is disabled on your controller, you can enable data scrubbing, but not through the ServeRAID Manager. Instead, use the IPSSEND command-line program. This program comes with the device option and is on the IBM ServeRAID Support CD. For more information, refer to the IBM ServeRAID-4 Ultra160 SCSI Controller User's Reference.

## More information

- Synchronizing logical drives (action)

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