Dell PowerVault MD3000 - Manual (Page 39)

Using Your RAID Enclosure
39
RAID Operations and Features
This section details the following RAID operations and features supported by your enclosure or RAID
controller:
• Virtual disk operations
• Disk group operations
• RAID background operations priority
• Virtual disk migration and roaming
Virtual Disk Operations
Virtual Disk Initialization
Every virtual disk must be initialized. Up to four concurrent initializations can occur for the same RAID
controller module.
Background Initialization
The RAID controller module executes a background initialization when the virtual disk is created to
establish parity, while allowing full host access to the virtual disks. Background initialization does not run
on RAID 0 virtual disks.
The background initialization rate is controlled by MD Storage Manager. You must stop an ongoing
background initialization before you change the rate, or the rate change will not take effect. After you
stop background initialization and change the rate, the rate change will take effect when the background
initialization restarts automatically.
NOTE:
Unlike initialization of virtual disks, background initialization does not clear data from the physical disks.
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, since the system does not have the redundancy to recover the data.