Uniwide Technologies UniServer 1522, User Manual

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5.2.2.3 IM/IME Description
The LSI Logic Integrated Mirroring (IM) feature supports one or two mirrored volumes on each LSI Logic
SAS controller (or one mirrored volume and one Integrated Striping volume). Typically, one of these volumes
is the boot volume, as shown in Figure. This is accomplished through the firmware of the LSI Logic SAS
controller that supports the standard Fusion-MPT interface. The runtime mirroring of the boot disk is transparent
to the BIOS, drivers, and operating system.
Host-based status software monitors the state of the mirrored disks and reports any error conditions.
In Figure, the system is configured with a second disk as a mirror of the first (primary) disk.
The advantage of Integrated Mirroring (RAID 1) is that there is always a mirrored copy of the data. The
disadvantage is that writes take longer because data must be written twice. On the other hand,
performance is actually improved during reads. Figure shows the logical view and physical view of an
Integrated Mirroring configuration with two disks in the mirrored volume.