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SAS2 Integrated RAID Solution User Guide Chapter 2: Overview of Integrated RAID Mirrored Volumes | Mirrored Volume Features
LSI Corporation Confidential
| August 2010 Page 11
2.4 Mirrored Volume Features 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.
2.4.1 Resynchronization with
Concurrent Host I/O Operation
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.
2.4.2 Hot Swapping 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.
2.4.3 Hot Spare Disk 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.
2.4.4 Online Capacity Expansion 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.
2.4.5 Media Verification 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.