RAID types without parity

RAID0

In fact, this is not a true RAID, because RAID0 doesn't have the redundancy. Lack of the redundancy causes RAID 0 stands among the arrays at the lowest level 0.

RAID level 0 utilizes striping technique in which the flow of data is split into the blocks of a certain size and then distributed onto the member disks evenly.

A minimum of two disks is required for a RAID0, and the array capacity is determined by the smallest member disk, the size of which is multiplied by the number of disks.

RAID 0 is used to improve the system performance due to read and write speed increase. RAID 0 array consisting of N disks provides N times faster reads and writes. Significant disadvantage of RAID 0 is that it doesn't provide fault tolerance at all. This means that it is impossible to recover array data if one of the member disks fails. Only RAW recovery can bring back scraps of short, unfragmented files. So, RAID 0 is a relatively inexpensive array with a minimum of two disks, the disk space of which is used entirely for user data (no redundancy). RAID 0 is usually used where it is required to increase the system performance for both read and write operations.

RAID 1

RAID 1 is based on mirroring technique where two copies of data are stored on the different array member disks.

Exactly two disks are required to create RAID 1, and the array capacity equals to the size of the smallest member disk. Theoretically, one can have a three-way mirror, holding three copies of data, but that is never used in production.

RAID 1 is designed to provide fault tolerance that is achieved by 100% redundancy of data. In case of a single disk failure, data can be recovered in full using the other member disk. 100% redundancy may result in read speed improvement provided that the read requests are distributed to all the RAID members evenly. Using such a technique one can improve the read speed by the factor of two.

Unlike RAID 0, twice as fast reads will be achieved for any query large enough, since each member disk contains identical copies of data. RAID 1 doesn't provide write speed improvement, because all copies of the newly arrived data must be updated.

RAID 0+1

This array is a result of a combination of RAID levels 0 and 1, hence it is based on the mirroring and striping techniques. A minimum of four disks is required to create RAID 0+1; firstly, two disks are used to create RAID 0 which is then mirrored to the rest of the array members.

The array capacity is determined by the smallest member disk multiplied by the number of the disks in the original RAID 0.

Read speed for RAID 0+1 consisting of N disks is N times faster than read speed in case of a single disk. This RAID level inherits performance of RAID 0 and RAID 1 and fault tolerance of RAID 1. RAID 0+1 is one of the expensive options of RAID per gigabyte storage because exactly half of the array capacity is used for the redundancy. The overhead to provide the redundancy increases with the number of disks.

It is easy to create RAID 0+1 from the existing RAID 0 because the conversion requires just a simple mirroring operation.

RAID 1+0

RAID 1+0 is the result of a combination of RAID levels 1 and 0, and hence uses mirroring and striping techniques. This array has all the characteristics of RAID 0+1. The only difference is that it is rarely possible to create RAID 1+0 from RAID 1 on-the-fly, since the complete restriping of the array is required.

Recovery considerations

From the RAID recovery point of view, RAID 0+1 is exactly the same as RAID 1+0. Even better, it is the same as RAID 0, because a full RAID 0+1 contains two identical subsets of member disks, each one being a complete RAID 0 with all the data.

For recovery, select all the RAID 0+1 member disks you have (typically, that's four disks) and search for RAID 0. ReclaiMe Free RAID Recovery will pick an arbitrary subset of the member disks forming a RAID 0 and determine its parameters. The detailed instrcutions on how to recover RAID10 manually or automatically are provided at the RAID10 recovery page.

RAID 0+1 or RAID 1+0 still contains a full RAID 0 subset even if one of the member disks is missing. In this case, ReclaiMe Free RAID Recovery will automaticaly pick a complete RAID 0 subset.