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3ware® User Guide > Maintaining Units > Background Tasks > Rebuilding Units

Rebuilding Units
This topic is organized into the following:
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Overview of Rebuilding
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 3DM 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 3DM, 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 RAID 5 or RAID 6 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 3DM 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 /dev/sda1.
Rebuilding a Unit Through 3DM
When a drive on a unit becomes defective, you replace it with an available drive and then rebuild the unit. If Auto Rebuild is enabled and a drive is available, starting the rebuild is optional as it will start automatically.
To rebuild a unit through 3DM
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In 3DM, choose Management > Maintenance.
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In the Unit Maintenance section of the Maintenance page, select the degraded unit and click the Rebuild Unit button.
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Show Selecting a Drive when Rebuilding
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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.
Rebuilding Units through 3BM
When a RAID unit becomes degraded, it is marked as such, and the drive(s) that failed are marked as Not In Use in the 3BM screens.
The next figure shows an example of how a degraded RAID 5 unit appears in 3BM.
Show Degraded RAID 5 Array to be Rebuilt
You can start the rebuild of a degraded unit manually in 3BM, or you can let the system boot and allow the rebuild to take place automatically.
The rebuild process will take less time if Rapid RAID Recovery has been enabled during unit creation. See Rapid RAID Recovery
To start the rebuild of a unit through 3BM
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A red message box informs you that the unit is degraded, and suggests some possible approaches. The next figure shows an example of a degraded-array message.
Show Degraded Disk Array Warning Message
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If your degraded unit has a drive indicated as Not in Use, the drive may still be usable. Try rebuilding with the Not in Use drive intact. Simply select the unit (highlight it and press Enter) and then select the Rebuild Unit button.
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When the Rebuild confirmation screen appears, confirm that you selected the correct unit by selecting OK.
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Press F8 to save your changes and exit 3BM. The unit will begin rebuilding after the operating system finishes loading.
If the rebuild fails and you have no available drives, do one of the following:
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If your system has hot swap bays, you can replace the failed or Not In Use drive and rescan (Alt-R) the unit.
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If your system does not have hot swap bays, power down the system and replace the failed or Not In Use drive. Then power on the system and restart 3BM.
Then follow these steps:
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An asterisk appears in the left most column to indicate the drive is selected.
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Press Tab to select the degraded unit and press Enter to select it.
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Tab to the Maintain Unit button and press Enter.
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Select Rebuild from the pop-up menu and press Enter.
Show Rebuild Option on the Maintain Menu
The Rebuild Disk Array screen displays.
Show Rebuild Disk Array Screen
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Press Enter to select the OK button to continue.
You are returned to the main screen; “Rebuilding” appears next to the unit you selected.
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Press F8 to save your changes and exit 3BM.
The unit will begin rebuilding about ten minutes after the operating system finishes loading and the 3ware driver has loaded.

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