Avago Technologies SAS 9300-4i Host Bus Adapter - Manual (Page 13)

LSI Corporation
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SAS-3 Integrated RAID Solution User Guide
November 2012 Chapter 2: Overview of Integrated RAID Mirrored Volumes
Mirrored Volume Features
2.4.6 Disk Write Caching
By default, the Integrated RAID firmware disables disk write caching for mirrored volumes to make sure that the write
journal entry stored in nonvolatile static RAM (NVSRAM) is always valid. If you enable disk write caching (not
recommended), you might cause the disk write log to be invalid.
2.4.7 NVSRAM Usage
The Integrated RAID firmware requires at least a 32-KB NVSRAM to perform write journaling for mirrored volumes on
LSI SAS-3 controllers. The NVSRAM also preserves configuration information across reboots. The firmware uses write
journaling to verify that the disks in the mirrored volume are synchronized with each other.
2.4.8 Background Initialization
Background initialization (BGI) is the process of copying data from primary to secondary disks in a mirrored volume.
The Integrated RAID firmware starts BGI automatically as a background task when it creates a volume. The volume
remains in the Optimal state while BGI is in progress.
2.4.9 Consistency Check
A consistency check is a background process that reads data from primary and secondary disks in a mirrored volume
and compares it to make sure the data is identical on both disks. Use the LSI SAS-3 BIOS Configuration Utility to run a
consistency check on a mirrored volume.
2.4.10 Make Data Consistent
If it is enabled in the Integrated RAID firmware, the make data consistent (MDC) process starts automatically and runs
in the background when you move a redundant volume from one LSI SAS-3 controller to another LSI SAS-3 controller.
MDC compares the data on the primary and secondary disks. If MDC finds inconsistencies, it copies data from the
primary disk to the secondary disk.