Avago Technologies MegaRAID Fast Path Software - Manual (Page 24)

Page 24 LSI Corporation Confidential | July 2011
MegaRAID SAS Software User Guide Chapter 2: Introduction to RAID | Components and Features
Typically, when a drive fails or is expected to fail, the data is rebuilt on a hot spare. The
failed drive is replaced with a new disk. Then the data is copied from the hot spare to
the new drive, and the hot spare reverts from a rebuild drive to its original hot spare
status. The copyback operation runs as a background activity, and the virtual drive is
still available online to the host.
Copyback is also initiated when the first Self-Monitoring Analysis and Reporting
Technology (SMART) error occurs on a drive that is part of a virtual drive. The
destination drive is a hot spare that qualifies as a rebuild drive. The drive with the
SMART error is marked as “failed” only after the successful completion of the copyback.
This situation avoids putting the drive group in Degraded status.
NOTE: During a copyback operation, if the drive group involved in the copyback is
deleted because of a virtual drive deletion, the destination drive reverts to an
Unconfigured Good state or hot spare state.
Order of Precedence.
In the following scenarios, rebuild takes precedence over the copyback operation:
 If a copyback operation is already taking place to a hot spare drive, and any virtual
drive on the controller degrades, the copyback operation aborts, and a rebuild
starts. The rebuild changes the virtual drive to the Optimal state.
 The rebuild operation takes precedence over the copyback operation when the
conditions exist to start both operations. For example:
— The hot spare is not configured (or unavailable) in the system.
— Two drives (both members of virtual drives) exist, with one drive exceeding the
SMART error threshold, and the other failed.
— If you add a hot spare (assume a global hot spare) during a copyback operation,
the copyback is aborted, and the rebuild operation starts on the hot spare.
2.4.6 Background Initialization Background initialization is a check for media errors on the drives when you create a
virtual drive. It is an automatic operation that starts five minutes after you create the
virtual drive. This check ensures that striped data segments are the same on all of the
drives in the drive group.
Background initialization is similar to a consistency check. The difference between the
two is that a background initialization is forced on new virtual drives and a consistency
check is not.
New RAID 5 virtual drives and new RAID 6 virtual drives require a minimum number of
drives for a background initialization to start. If there are fewer drives, the background
initialization does not start. The background initialization needs to be started manually.
The following number of drives are required:
— New RAID 5 virtual drives must have at least five drives for background
initialization to start.
— New RAID 6 virtual drives must have at least seven drives for background
initialization to start.