LSI SAS2 manual Mirrored Volume Features

SAS2 Integrated RAID Solution User Guide Chapter 2: Overview of Integrated RAID Mirrored Volumes Mirrored Volume Features

2.4 Mirrored Volume Features

2.4.1Resynchronization with Concurrent Host I/O Operation

2.4.2Hot Swapping

2.4.3 Hot Spare Disk

2.4.4 Online Capacity Expansion

2.4.5 Media Verification

This section describes features of Integrated Mirroring, Integrated Mirroring + Striping, and Integrated Mirroring Enhanced volumes. You can configure one or two mirrored volumes on each LSI SAS2 controller.

The Integrated RAID firmware allows host I/O transactions to continue on a mirrored volume while it resynchronizes the volume in the background. The firmware automatically starts resynchronizing data after a disk failure activates a hot spare, or after a disk in a mirrored volume has been hot swapped.

The Integrated RAID firmware supports hot swapping, and it automatically resynchronizes the hot-swapped disk in the background without any host or user intervention. The firmware detects hot-swap removal and disk insertion.

Following a hot-swap event, the firmware verifies that the new physical disk has enough capacity for the mirrored volume. The firmware resynchronizes all replaced hot-swapped disks, even if the same disk is re-inserted. In a mirrored volume with an even number of disks, the firmware marks the hot-swapped disk as a secondary disk and the other disk with data as the primary disk. The firmware resynchronizes all data from the primary disk onto the new secondary disk. In a mirrored volume with an odd number of disks, primary and secondary sets include three disks instead of two.

You can configure two disks as global hot spare disks to protect data on the mirrored volumes configured on the SAS2 controller. If the Integrated RAID firmware fails one of the mirrored disks, it automatically replaces the failed disk with a hot spare disk and then resynchronizes the mirrored data. The firmware automatically receives a notification when a hot spare replaces the failed disk, and it then designates that disk as the new hot spare.

The OCE feature enables you to expand the capacity of an existing two-disk Integrated Mirroring (RAID 1) volume by replacing the original disk drives with higher-capacity drives that have the same protocol (SAS or SATA).

NOTE: The new drives must have at least 50 GB more capacity than the original drives of the volume.

After you replace the disk drives and run the OCE command, you must use a commercial tool specific to the operating system to move or increase the size of the partition on the volume.

The Integrated RAID firmware supports a background media verification feature that runs at regular intervals when the mirrored volume is in the Optimal state. If the verification command fails for any reason, the firmware reads the other disk’s data for this segment and writes it to the failing disk in an attempt to refresh the data. The firmware periodically writes the current media verification logical block address to nonvolatile memory so that the media verification can continue from where it stopped prior to a power cycle.

LSI Corporation Confidential August 2010 Page 11