Redundant Array of Independent Disks (RAID) describes a storage solution in which part of the storage capacity stores redundant information about user data that is stored on the remainder of the storage capacity. The redundant information enables regeneration of user data if one of the disk physical disks in the fails.
RAID relies on a series of configurations, called levels, to determine how user data and data are written to and retrieved from the disk physical disks.
RAID 1/10, RAID 3, RAID 5, and RAID 6 write redundancy data to the disk physical disk media for fault tolerance. The redundancy data might be a copy of the data (mirrored) or an error-correcting code derived from the data. You can use the redundancy data to quickly reconstruct information on a replacement disk physical disk if a disk physical disk fails.
You configure a single RAID level across a single disk group. All redundancy data for that disk group is stored within the disk group. The capacity of the disk group is the aggregate capacity of the member disk physical disks, minus the capacity that is reserved for redundancy data. The amount of capacity needed for redundancy depends on the RAID level used. Select Disk Group >> Change >> RAID Level when you want to change the redundancy of the disk group (such as changing from RAID 0 to RAID 5).
This storage management software offers the following RAID level configurations: RAID 0, RAID 1 or RAID 10, RAID 3, RAID 5, or RAID 6. These RAID levels are described in the following table. Each RAID level provides different performance features, which are described in RAID Levels and Performance.
RAID Level
Short Description
Details
RAID 0
Non-redundant, Striping mode
How it works:
RAID 0 stripes data across all of the disk physical disks in the disk group.
Data protection features:
RAID 0 is not recommended for high availability needs. RAID 0 is better for non-critical data.
If a single disk physical disk fails in the disk group, all of the associated fail, and all data is lost.
Disk physical disk number requirements:
RAID 0 and RAID 1 disk groups can have more than 30 disk physical disks. A disk group can be created that includes all the disk physical disks in the storage system.
RAID 1/10 or RAID 10
Striping/Mirroring mode
How it works:
RAID 1/10 uses disk mirroring to write data to two duplicate disk disks simultaneously.
RAID 10 uses disk physical disk striping to stripe data across a set of mirrored disk physical disk pairs.
Data protection features:
RAID 1/10 and RAID 10 offer high performance and the best data availability.
RAID 1/10 and RAID 10 use disk physical disk mirroring to make an exact copy from one disk physical disk to another disk physical disk.
If one of the disk physical disks in a disk physical disk pair fails, the can instantly switch to the other disk physical disk without any loss of data or service.
A single disk physical disk failure causes associated virtual disks to become degraded. The mirror disk physical disk allows access to the data.
A disk physical disk-pair failure in a disk group causes all of the associated virtual disks to fail, and data loss could occur.
Disk physical disk number requirements:
A minimum of two disk physical disks is required for RAID 1: one disk physical disk for the user data, and one disk physical disk for the mirrored data.
If you select four or more disk physical disks, RAID 10 is automatically configured across the disk group: two disk physical disks for user data, and two disk physical disks for the mirrored data.
You must have an even number of disk physical disks in the disk group. If you do not have an even number of disk physical disks and you have some remaining unassigned disk physical disks, select Disk Group >> Add Free Capacity to add additional disk physical disks to the disk group, and retry the operation.
RAID 0 and RAID 1 disk groups can have more than 30 disk physical disks. A disk group can be created that includes all the disk physical disks in the storage system.
RAID 3
High Bandwidth mode
How it works:
User data and redundant information (consistency) is striped across the disk physical disks.
The equivalent of one disk physical disk's worth of capacity is used for redundant information.
Data protection features:
If a single disk physical disk fails in a RAID 3 disk group, all associated virtual disks become degraded but the redundant information allows the data to still be accessed.
If two or more disk physical disks fail in a RAID 3 disk group, all associated virtual disks fail, and all data is lost.
Disk physical disk number requirements:
You must have a minimum of three disk physical disks in the disk group.
Typically, you are limited to a maximum of 30 disk physical disks in the disk group.
RAID 5
High I/O mode
How it works:
User data and redundant information (consistency) is striped across the disk physical disks.
The equivalent capacity of one disk physical disk is used for redundant information.
Data protection features:
If a single disk physical disk fails in a RAID 5 disk group, all of the associated virtual disks become degraded. The redundant information allows the data to still be accessed.
If two or more disk physical disks fail in a RAID 5 disk group, all of the associated virtual disks fail, and all data is lost.
Disk physical disk number requirements:
You must have a minimum of three disk physical disks in the disk group.
Typically, you are limited to a maximum of 30 disk physical disks in the disk group.
RAID 6
High I/O mode
How it works:
User data and redundant information (consistency) is striped across the disk physical disks.
The equivalent capacity of two disk physical disks is used for redundant information.
Data protection features:
If two disk physical disks fail in a RAID 6 disk group, all of the associated virtual disks become degraded, but the redundant information allows the data to still be accessed.
If three or more disk physical disks fail in a RAID 6 disk group, all of the associated virtual disks fail, and all data is lost.
Disk physical disk number requirements:
You must have a minimum of five disk physical disks in the disk group.
Typically, you are limited to a maximum of 30 disk physical disks in the disk group.