Dell MD3000 RAID Operations and Features, Virtual Disk Operations, Background Initialization

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.

Using Your RAID Enclosure

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