7-5
Chapter 7: Integrated Mirroring and Integrated Mirroring Enhanced
Following a hot swap event, the firmware readies the new physical disk by spinning it up
and verifying that it has enough capacity for the mirrored volume. The firmware
resynchronizes all hot-swapped disks that have been removed, even if the same disk is
re-inserted. In a two-disk mirrored volume, the firmware marks the hot-swapped disk as
the secondary disk and marks the other mirrored disk as the primary disk. The firmware
resynchronizes all data from the primary disk onto the new secondary disk.
SMART Support
SMART is a technology that monitors hard disk drives for signs of future disk failure and
generates an alert if such signs are detected. The firmware polls each physical disk in
the volume at regular intervals. If the firmware detects a SMART ASC/ASCQ code on a
physical disk in the IM/IME volume, it processes the SMART data and stores it in
nonvolatile memory. The IM/IME volume does not support SMART directly, since it is
just a logical representation of the physical disks in the volume.
Hot Spare Disk
One or two disk drives per controller can be configured as global hot spare disks, to
protect data on the IM/IME volumes configured on the controller. If the 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 is automatically notified when the
failed disk has been replaced, and it then designates the failed disk as the new hot
spare.
Media Verification
The firmware supports a background media verification feature that runs at regular
intervals when the IM/IME volume is in optimal state. If the verification command fails for
any reason, the other disk’s data for this segment is read and written to the failing disk in
an attempt to refresh the data. The current Media Verification Logical Block Address is
written to nonvolatile memory occasionally to allow media verification to continue
approximately where it left off prior to a power-cycle.
Disk Write Caching
The firmware disables disk write caching by default for IM/IME volumes. This is done to
increase data integrity, so that the disk write log stored in NVSRAM is always valid. If
disk write caching were enabled (not recommended), the disk write log could be invalid.
NVSRAM Usage
The Integrated RAID firmware requires at least a 32K NVSRAM in order to perform write
journaling. Write journaling is used to verify that the disks in the IM/IME volume are
synchronized with each other.