RAID - Non-standard Levels

Non-standard Levels

Many configurations other than the basic numbered RAID levels are possible, and many companies, organizations, and groups have created their own non-standard configurations, in many cases designed to meet the specialised needs of a small niche group. Most of these non-standard RAID levels are proprietary.

• Himperia is using RAID 50EE in ZStore 3212L product. This is a RAID 0 of two pools with RAID 5EE (7+1+1). It is tolerant up to 2 disks failures at the same time, and up to 4 disks failures in degrade mode. Reconstruction time is set to a minimum thanks to RAID 5EE. And performance is increased, thanks to RAID 0.
• Storage Computer Corporation used to call a cached version of RAID 3 and 4, RAID 7. Storage Computer Corporation is now defunct.
• EMC Corporation used to offer RAID S as an alternative to RAID 5 on their Symmetrix systems. Their latest generations of Symmetrix, the DMX and the V-Max series, do not support RAID S (instead they support RAID 1, RAID 5 and RAID 6.)
• The ZFS filesystem, available in Solaris, OpenSolaris and FreeBSD, offers RAID-Z, which solves RAID 5's write hole problem.
• Hewlett-Packard's Advanced Data Guarding (ADG) is a form of RAID 6.
• NetApp's Data ONTAP uses RAID-DP (also referred to as "double", "dual", or "diagonal" parity), is a form of RAID 6, but unlike many RAID 6 implementations, it does not use distributed parity as in RAID 5. Instead, two unique parity drives with separate parity calculations are used. This is a modification of RAID 4 with an extra parity drive.
• Accusys Triple Parity (RAID TP) implements three independent parities by extending RAID 6 algorithms on its FC-SATA and SCSI-SATA RAID controllers to tolerate a failure of 3 drives.
• Linux MD RAID10 (RAID 10) implements a general RAID driver that defaults to a standard RAID 1 with 2 drives, and a standard RAID 1+0 with four drives, but can have any number of drives, including odd numbers. MD RAID 10 can run striped and mirrored, even with only two drives with the f2 layout (mirroring with striped reads, giving the read performance of RAID 0; normal Linux software RAID 1 does not stripe reads, but can read in parallel).
• Hewlett-Packard's EVA series arrays implement vRAID - vRAID-0, vRAID-1, vRAID-5, and vRAID-6; vRAID levels are closely aligned to Nested RAID levels: vRAID-1 is actually a RAID 1+0 (or RAID 10), vRAID-5 is actually a RAID 5+0 (or RAID 50), etc.
• IBM (among others) has implemented a RAID 1E (Level 1 Enhanced). It requires a minimum of 3 drives. It is similar to a RAID 1+0 array, but it can also be implemented with either an even or odd number of drives. The total available RAID storage is n/2.
• Hadoop has a RAID system that generates a parity file by xor-ing a stripe of blocks in a single HDFS file.