Learn About RAID Levels and Data Protection
Related Topics
RAID (Redundant Array of Independent Disks) describes a storage solution in which part of the storage capacity is used to store redundant information about user data stored on the remainder of the storage capacity. The redundant information enables regeneration of user data if one of the disk drives in the array fails.
RAID relies on a series of configurations, called levels, to determine how user and redundancy data is written and retrieved from the drives.
RAID levels 1, 3, and 5 write redundancy data to the drive media for fault tolerance. The redundancy data might be a copy of the data (mirrored) or an error-correcting code derived from the data. The redundancy data can be used to quickly reconstruct information on a replacement drive if a drive fails.
You configure a single RAID level across a single array. All redundancy data for that array is stored within the array. The capacity of the array is the aggregate capacity of the member drives, minus the capacity reserved for redundancy data. The amount of capacity needed for redundancy depends on the RAID level used. Use the Array >> Change >> RAID Level option when you want to change the array's redundancy (such as changing from RAID 0 to RAID 5).
This storage management software offers four formal RAID level configurations: RAID level 0, 1, 3, and 5 described in the table below. Each RAID level provides different performance features, described in Learn About RAID Levels and Performance.
RAID Level
|
Short Description
|
Details
|
RAID 0
|
Non-redundant, Striping Mode
|
How It Works
- RAID level 0 stripes data across all of the drives in the array.
Data Protection Features
- RAID level 0 is not recommended for high availability needs. RAID 0 is better for non-critical data.
- If a single drive fails in the array, all associated logical drives fail and all data is lost.
Drive Number Requirements
- Typically, you are limited to a maximum of 30 drives in the array.
|
RAID 1
|
Striping/Mirroring Mode
|
How It Works
- RAID 1 is also called RAID 10 or 0+1.
- RAID 1 uses disk mirroring to make an exact copy from one drive to another drive.
Data Protection Features
- RAID 1 offers the best data availability but only half of the drives in the array are available for user data.
- If a single drive fails in a RAID 1 array, all associated logical drives become degraded but the mirror drive allows the data to still be accessed.
- RAID 1 can survive multiple drive failures as long as no more than one failure exists per mirrored pair.
- If a drive-pair fails in a RAID 1 array, all associated logical drives fail and all data is lost.
Drive Number Requirements
- You must have an even number of drives in the array. If you do not have an even number of drives and you have some remaining unassigned drives, use the Array >> Add Free Capacity option to add additional drives to the array, then retry the operation.
- Typically, you are limited to a maximum of 30 drives in the array.
|
RAID 3
|
High Bandwidth Mode
|
How It Works
- User data and redundant information (parity) is striped across the drives.
- The equivalent of one drive's worth of capacity is used for redundant information.
Data Protection Features
- If a single drive fails in a RAID 3 array, all associated logical drives become degraded but the redundant information allows the data to still be accessed.
- If two or more drives fail in a RAID 3 array, all associated logical drives fail and all data is lost
Drive Number Requirements
- You must have a minimum of 3 drives in the array.
- Typically, you are limited to a maximum of 30 drives in the array.
|
RAID 5
|
High I/O Mode
|
How It Works
- User data and redundant information (parity) is striped across the drives.
- The equivalent of one drive's worth of capacity is used for redundant information.
Data Protection Features
- If a single drive fails in a RAID 5 array, all associated logical drives become degraded but the redundant information allows the data to still be accessed.
- If two or more drives fail in a RAID 5 array, all associated logical drives fail and all data is lost.
Drive Number Requirements
- You must have a minimum of 3 drives in the array.
- Typically, you are limited to a maximum of 30 drives in the array.
|
Related Topics
Learn About RAID Levels and Performance
Changing the RAID Level of an Array