RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple physical drives into a single logical unit to provide data redundancy and improve the performance of disk input/output operations. While there are several standard RAID levels, some companies have developed proprietary non-standard RAID levels that differ significantly from the standard levels.
| RAID Level | Description | Key Features | Limitations | When to Use |
|---|---|---|---|---|
| Double Parity | Uses two sets of parity data to protect against the failure of two drives in the array | Increased data protection | Reduced performance and capacity due to additional parity data | When high levels of data protection are required |
| RAID-DP | Proprietary implementation of double parity developed by NetApp | High levels of data protection and availability | Reduced performance and capacity compared to other RAID levels | When high levels of data protection and availability are required |
| RAID 1.5 | Variant of RAID 1 that stripes data and parity across multiple drives | Improved performance compared to RAID 1 | Only able to withstand the failure of a single drive | When a balance of performance and data protection is required |
| RAID 5E, 5EE, 6E | Variants of RAID 5 or RAID 6 with an integrated hot-spare drive | Improved performance and data protection | Spare drive cannot be shared among multiple arrays | When high levels of performance and data protection are required |
| RAID-7 | Trademark of Storage Computer Corporation that adds caching to a derivative of RAID 3 and RAID 4 | Improved performance | Not a standard RAID level | When improved performance is required |
| RAID S or Parity RAID | Proprietary striped parity RAID system developed by EMC Corporation | Flexibility in combining multiple volumes for parity purposes | Not a standard RAID level | When using EMC Symmetrix storage systems |
| Intel Matrix RAID | Feature that utilizes two physical disks and assigns part of each to a level 0 and level 1 array | Increased protection for operating system, programs, and data | Not a standard RAID level | When increased protection for operating system, programs, and data is required |
| Linux MD RAID 10 | RAID level implemented in Linux's Multiple Device (MD) driver | Improved performance and data protection | Higher cost due to requirement for at least four drives | When high levels of performance and data protection are required |
| IBM ServeRAID 1E | Proprietary RAID level developed by IBM that is similar to RAID 10 | Improved performance and data protection | Not a standard RAID level | When using IBM server systems and a balance of performance and data protection is required |
| RAID K | Proprietary RAID level developed by LSI Logic that is similar to RAID 5, but uses a dedicated parity disk | Improved performance compared to RAID 5 | Not a standard RAID level | When using LSI Logic storage systems and improved performance is required |
| RAID Z | Proprietary RAID level developed by Sun Microsystems that is similar to RAID 5, but uses a dynamic stripe width | Improved performance compared to RAID 5 | Not a standard RAID level | When using Sun Microsystems storage systems and improved performance is required |
| UNRAID | Proprietary RAID level developed by Lime Technology that allows users to mix and match drives of different sizes and speeds in a single array | Flexibility in hardware configuration | Not a standard RAID level | When using Lime Technology storage systems and flexibility in hardware configuration is required |
| Drive Extender | Proprietary RAID level developed by Microsoft that is used in the Windows Home Server operating system | Increased capacity and data protection | Not a standard RAID level | When using the Windows Home Server operating system and increased capacity and data protection is required |
Double parity is a non-standard RAID level that involves the use of two sets of parity data to protect against the failure of two drives in the array. This can provide increased data protection compared to standard RAID levels, but can also come at a cost of reduced performance and capacity due to the additional parity data that must be written and read.
RAID-DP is a proprietary implementation of double parity developed by NetApp for use in their storage systems. It is designed to provide high levels of data protection and availability, but may come at a cost of reduced performance and capacity compared to other RAID levels.
RAID 1.5, also known as RAID 1E, is a variant of RAID 1 that stripes data and parity across multiple drives rather than mirroring data on separate drives. This can provide improved performance compared to RAID 1, but does not offer the same level of data protection since it is only able to withstand the failure of a single drive.
RAID 5E, RAID 5EE and RAID 6E (with the added E standing for Enhanced) generally refer to variants of RAID 5 or RAID 6 with an integrated hot-spare drive, where the spare drive is an active part of the block rotation scheme. This allows the I/O to be spread across all drives, including the spare, thus reducing the I/O bandwidth per drive, allowing for higher performance. It does, however, mean that a spare drive cannot be shared among multiple arrays, which is occasionally desirable. The scheme was introduced by IBM ServeRAID around 2001.
RAID 7 is a trademark of Storage Computer Corporation. It adds caching to a derivative of RAID 3 and RAID 4 to improve performance.
RAID S is EMC Corporation's proprietary striped parity RAID system used in their Symmetrix storage systems. Each volume exists on a single physical disk, and multiple volumes are arbitrarily combined for parity purposes. EMC originally referred to this capability as RAID S, and then renamed it Parity RAID for the Symmetrix DMX platform. EMC now offers standard striped RAID 5 on the Symmetrix DMX as well. RAID-S is not used anymore in EMC products (except for products already sold).
Matrix RAID is a feature that first appeared in the Intel ICH6R RAID BIOS. It is not a new RAID level. Matrix RAID utilizes two physical disks. Part of each disk is assigned to a level 0 array, the other part to a level 1 array. Currently, most (all?) of the other cheap RAID BIOS products only allow one disk to participate in a single array. The recommended (by Intel) setup is to put the operating system, critical application programs and data on the RAID 1 volume. The thinking being that protection from losing the configured OS, programs and data is more important than a performance increase. Mostly, the RAID 0 volume in Matrix RAID is promoted for working with large files, such as videos during editing, and for no other reason.
Linux MD RAID 10, also known as RAID 10, is a software RAID level that combines striping (RAID 0) with mirroring (RAID 1). It involves the creation of two or more pairs of mirrored drives, with data striped across the pairs. This provides both improved performance through striping and data protection through mirroring. However, the capacity of the array is reduced by the space required for the mirrored drives.
IBM ServeRAID 1E is a proprietary RAID level developed by IBM for use in their ServeRAID controllers. It is similar to RAID 1.5 in that it stripes data and parity across multiple drives, but also includes support for a hot spare drive. This can provide improved performance and data protection compared to standard RAID 1, but is not as robust as other RAID levels that can withstand the failure of multiple drives.
RAID K is a proprietary RAID level developed by Promise Technology for use in their storage systems. It is similar to RAID 5, but uses a different algorithm for calculating parity that is optimized for small-block writes. This can improve performance when working with small files, but may come at a cost of reduced capacity due to the additional parity data that must be stored.
RAID Z is a proprietary RAID level developed by Sun Microsystems for use in their Solaris operating system. It is similar to RAID 5, but uses a different algorithm for calculating parity that allows for the use of disks of different sizes in the same array. This can provide more flexibility in terms of capacity, but may come at a cost of reduced performance compared to standard RAID 5.
Unraid is a proprietary RAID-like system developed by Lime Technology that allows users to mix and match drives of different sizes and types in a single array. It uses a technique called "disk pooling" to create a single logical volume from the available drives, and allows users to configure a designated "parity" drive to provide data protection. However, unlike traditional RAID levels, Unraid does not stripe data across drives, which can impact performance when working with large files.
Drive Extender is a proprietary feature developed by Microsoft for use in their Windows Home Server operating system. It allows users to combine multiple drives into a single logical volume, with the system automatically moving and balancing data across the drives to optimize space usage. It provides some data protection through the use of redundant copies of data, but is not a traditional RAID level and does not stripe data across drives or use parity for data protection.
Non-standard RAID levels are proprietary RAID configurations that differ significantly from the standard levels. These configurations may offer unique features or improved performance, but they can also present challenges in the event of data loss. Non-standard RAID configurations may not be recognized by standard data recovery tools, making it more difficult to recover data. If you experience data loss on a non-standard RAID configuration, it is recommended to seek out a reputable data recovery service. RAID data recovery experts will have the necessary tools, knowledge, and expertise to handle hard drives with non-standard RAID configurations, and these factors will greatly increase the chances of a successful recovery.
"RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple physical drives into a single logical unit to provide data redundancy and improve the performance of disk input/output operations." (Wikipedia)
"Non-standard RAID levels are proprietary RAID configurations that differ significantly from the standard levels. These configurations may offer unique features or improved performance, but they can also present challenges in the event of data loss." (Backblaze)
"Non-standard RAID configurations may not be recognized by standard data recovery tools, making it more difficult to recover data." (Wikipedia)
"RAID Levels: Definition and Comparison" (Backblaze)
"RAID Configuration Best Practices" (NetApp)
"RAID Technology Overview" (Intel)