Rebuilding Units

Rebuilding is the process of generating data on a new drive after it is put into service to replace a failed drive in a fault tolerant unit.

If a hot spare of the appropriate drive type (SAS or SATA) is specified and a redundant unit degrades, it will be used to automatically replace the failed drive in the redundant unit without intervention on your part. The rebuild process will automatically be launched as a background process at the next scheduled time. If scheduling is turned off, the rebuild process will start almost immediately (within a couple of minutes). If 3DM2 is running and E-mail notification is enabled, an event notification will be sent to specified users when the unit degrades and again when the rebuild process is complete.

If the Auto-Rebuild policy is enabled (see Setting the Auto-Rebuild Policy), the firmware will attempt to rebuild a degraded unit with an available drive or a failed drive.

If desired, you can manually replace the drive, rescan the controller, and start the rebuild process. Manual rebuilds can be started from either 3BM, CLI, or 3DM2, although the rebuild itself only happens when the operating system is running.

The rebuild process may take less time if Rapid RAID Recovery has been enabled during unit creation. See Rapid RAID Recovery.

Rebuilds on multiple units can take place simultaneously.

If multiple drives are faulted in a RAID 10 configuration, the drives are rebuilt simultaneously. In a 4-drive RAID 10 configuration, up to two drives can be rebuilt. In a 6-drive configuration, up to three drives can be rebuilt. In an 8-drive configuration, up to four drives can be rebuilt. In a 12-drive configuration, up to six drives can be rebuilt.


	Note: If both drives in a RAID 10 mirrored set are faulted, the data is not recoverable. Up to half of the drives in a RAID 10 unit can become defective and still have the user data retained, as long as the failed drives are only half of each mirrored pair.

A RAID 5 unit can have one drive fail before becoming inoperable.

A RAID 50 unit can sustain multiple drive failures, as long there is only one failed drive in each RAID 5 set.

A RAID 6 unit can have two simultaneous drive failures, before becoming inoperable.

When a redundant RAID unit is running in Degraded mode and you rebuild it, the missing data is reconstructed from all functioning drives.

Note: If a rebuild fails, check the Alarms page for the reason. If there was an ECC error on the source disk, you can force the rebuild to continue by checking the Overwrite ECC policy on the Controller Settings page in 3DM2 and then running Rebuild again. This will cause uncorrectable blocks to be rewritten and the data may be incorrect. It is recommended that you execute a file system check when the rebuild completes.

•	Under Windows, you can do this by right-clicking on the Drive and choosing Properties; then on the Tools tab, click Check Now.

•	Under Linux or FreeBSD use fsck

•	On Mac OS X, you can do this using the First Aid tab in the Disk Utility—select the disk on the left and then click Verify Disk. If verification encounters problems, you can then use the Repair Disk option on the same screen.

•	For OpenSolaris and VMware you should follow your operating system’s guide to perform a file system check.

To rebuild a unit through 3DM2

1	If necessary, add a new drive to replace the failed drive. (For details, see Adding a Drive.)

2	In 3DM2, choose Management >> Maintenance.

3	In the Unit Maintenance section of the Maintenance page, select the degraded unit and click the Rebuild Unit button.

4	When a dialog box displays available drives, select the drive you want to replace the failed drive and click OK.

Show Selecting a Drive when Rebuilding

5	If the degraded unit has more than one failed drive (for example, a RAID 10 where both mirrored pairs each have a failed drive), repeat step 3 and step 4 to select another drive.

If rebuild scheduling is not enabled on the Scheduling page, the rebuild process begins almost immediately in the background. If rebuild scheduling is enabled, the unit will not start actively rebuilding until the next scheduled time.


	Note: If you need to cancel a rebuild, you can do so by using the Remove Drive link on the Maintenance page to remove the drive from the unit.

Related Topics: Cancelling a Rebuild and Restarting It with a Different Drive