Dell PowerVault MD3220i Owner's Manual - Page 40

Disk groups are always created in the unconfigured capacity of a storage array. Unconfigured capacity is the available physical disk space not already assigned in the storage array. Virtual disks are created within the free capacity of a disk group. Free capacity is the space in a disk group that has not been assigned to a virtual disk. Virtual Disk States The storage array recognizes the following virtual disk states. Table 4-2. RAID Controller Virtual Disk States State Optimal Degraded Offline Force online Description The virtual disk contains physical disks that are all online. The virtual disk with a redundant RAID level contains an inaccessible physical disk. The system can still work properly, but performance may be affected and additional disk failures may result in data loss. A virtual disk with one or more member disks in an inaccessible (failed, missing, or offline) state. Data on the virtual disk is no longer accessible. The storage array forces a virtual disk that is in an Offline state to an Optimal state. If all the member physical disks are not available, the storage array forces the virtual disk to a Degraded state. The storage array can force a virtual disk to an Online state only when a sufficient number of physical disks are available to support the virtual disk. RAID Levels RAID levels determine the way in which data is written to physical disks. Different RAID levels provide different levels of accessibility, redundancy, and capacity. Using multiple physical disks has the following advantages over using a single physical disk: • Placing data on multiple physical disks (striping) allows input/output (I/O) operations to occur simultaneously and improve performance. • Storing redundant data on multiple physical disks using mirroring or parity supports reconstruction of lost data if an error occurs, even if that error is the failure of a physical disk. 40 Planning: MD3200i Series Storage Array Terms and Concepts