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36 Using Your RAID Enclosure
Foreground Initialization
The RAID controller module firmware supports full foreground initialization
for virtual disks. All access to the virtual disk is blocked during the
initialization process. During initialization, zeros (0x00) are written to every
sector of the virtual disk. The virtual disk is available after the initialization is
completed without requiring a RAID controller module restart.
Consistency Check
A consistency check verifies the correctness of data in a redundant array
(RAID levels 1, 5, and 10). For example, in a system with parity, checking
consistency means computing the data on one physical disk and comparing
the results to the contents of the parity physical disk.
A consistency check is similar to a background initialization. The difference is
that background initialization cannot be started or stopped manually, while
consistency check can.
NOTE: Dell recommends that you run data consistency checks on a redundant
array at least once a month. This allows detection and automatic replacement of
unreadable sectors. Finding an unreadable sector during a rebuild of a failed
physical disk is a serious problem, because the system does not have the
redundancy to recover the data.
Media Verification
Another background task performed on the RAID controller module is media
verification of all configured physical disks in a disk group. The RAID
controller module uses the Read operation to perform verification on the
space configured in virtual disks and the space reserved by the controller for
the metadata.
Cycle Time
The media verification operation runs only on selected disk groups,
independent of other disk groups. Cycle time is how long it takes to complete
verification of the metadata region of the disk group and all virtual disks in
the disk group for which media verification is configured. The next cycle for a
disk group starts automatically when the current cycle completes. You can set
the cycle time for a media verification operation between 1 and 30 days. The
firmware throttles the media verification I/O accesses to disks based on the
cycle time.