Dell POWERVAULT MD3620I - Manual (Page 44)

44 Planning: MD3600i Series Storage Array Terms and Concepts
Foreground Initialization
The storage array supports foreground initialization for virtual disks. All
access to the virtual disk is blocked during foreground initialization. During
foreground initialization, zeros (0x00) are written to every sector of the virtual
disk. The virtual disk is available after foreground initialization is completed.
Consistency Check
A consistency check verifies the correctness of data in a redundant array
(RAID levels 1, 5, 6, and 10). For example, in a system with parity, checking
consistency involves 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: It is recommended 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 by the storage array is media verification
of all configured physical disks in a disk group. The storage array uses the
Read operation to perform verification on the space configured in virtual
disks and the space reserved for the metadata.
Cycle Time
The media verification operation runs only on selected disk groups,
independent of other disk groups. Cycle time is the time taken 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
storage controller throttles the media verification I/O accesses to disks based
on the cycle time.
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