User`s guide

12 Integrated Mirroring Overview
www.dell.com | support.dell.com
Resynchronization with Concurrent Host I/O Operation
Resynchronization is attempted after the firmware has been reset, or after a “hot swap” has
occurred to one of the physical IM disks.
The IM volume can be partially resynchronized, if the logging information in NVSRAM indicates
that this is necessary. It usually takes less than a second for the firmware to complete a partial
resynchronization. Like full synchronization, partial resynchronization is performed in the
background.
Metadata Support
Metadata is the data on each member disk describing the IM logical drive configuration. When the
firmware is initialized, each member disk is queried to read the stored metadata for consistency
checking. The usable disk space for each IM member disk is adjusted down to leave room for this
data.
Hot Swap
The IM firmware supports hot swapping . The hot-swapped disk is automatically resynchronized in
the background, without any host or user intervention. The hot swapped disk must be at the same
physical SCSI ID as one of the physical disks configured in the IM volume. The firmware detects
“hot swap” removal and disk insertion.
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 IM volume. The IM 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 IM 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
The IM firmware enables Mode 6 SMART on the IM member disks. Mode 6 SMART requires each
physical disk to be polled once per minute. If a SMART ASC/ASCQ code is detected on a physical
IM disk, the firmware processes the SMART data, and the last received SMART ASC/ASCQ is
stored in non-volatile memory. The IM volume does not support SMART directly, since it is just a
logical representation of the physical disks in the volume.
Media Verification
The IM firmware supports a background media verification feature that runs once per minute when
the IM volume is in optimal mode. The media verification feature issues a SCSI Verify command
to a segment of the disk. If the 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 non-volatile memory occasionally to allow Media
Verification to continue approximately where it left off prior to a power-cycle.