Avago Technologies SAS 9300-4i Host Bus Adapter - Manual (Page 12)

LSI Corporation
- 12 -
SAS-3 Integrated RAID Solution User Guide
November 2012 Chapter 2: Overview of Integrated RAID Mirrored Volumes
Mirrored Volume Features
2.4 Mirrored Volume Features
This section describes features of Integrated Mirroring volumes, Integrated Mirroring + Striping volumes, and
Integrated Mirroring Enhanced volumes.
2.4.1 Resynchronization with Concurrent Host I/O Operation
The Integrated RAID firmware permits 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 removed and then
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 disks.
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 SAS-3
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).
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 the media verification can
continue from where it stopped prior to a power cycle.
NOTE The replacement drives must have at least 50 GB more capacity than the original drives of the volume.