## About Virtual Disks

Redundant Array of Independent Disks (RAID) systems provide storage by making the data on many small disks readily available to file servers, hosts, or the network as a single array. RAID systems use two or more drives in combination for fault tolerance and performance. One of the factors in data throughput and availability is how the data is stored within the array, that is, the array's RAID level.

On the system, disk drives within a tray are grouped together into RAID sets, also called virtual disks, according to their RAID level. The storage arrays support the following RAID levels:

- RAID-0 - Provides data striping across multiple disks, but no redundancy. This improves performance but does not deliver fault tolerance.
- RAID-1 - Provides disk mirroring so that all data is copied to a separate disk.
- RAID-5 - Provides data striping at the byte level as well as stripe error correction (parity checking) information. This is the system's default RAID level. For this level, the minimum number of drives is three.

RAID-5 results in excellent performance and good fault tolerance. Parity checking specifies that when the RAID controller writes information onto disks, it also writes redundant information called parity bits. If a disk fails, the parity information enables the RAID controller to re-create the lost information as it is requested. Since the parity information is spread across multiple disks, only a percentage of the disks is used for parity information, which improves the efficiency of available storage space.

### Related Topics

- Configuring Storage Profiles
- Displaying Virtual Disk Information