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Diagram of a RAID 1 setup. RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks.This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk.
RAID 01, also called RAID 0+1, is a RAID level using a mirror of stripes, achieving both replication and sharing of data between disks. [3] The usable capacity of a RAID 01 array is the same as in a RAID 1 array made of the same drives, in which one half of the drives is used to mirror the other half.
Internally it uses a mix of techniques similar to RAID 1 and 5. Depending on the fraction of data in relation to capacity, it can survive up to three drive failures, [citation needed] if the "array" can be restored onto the remaining good disks before another drive fails. The amount of usable storage can be approximated by summing the ...
RAID stands for redundant array of independent disks (or, formerly, redundant array of inexpensive disks). RAID levels may refer to: Standard RAID levels , all the RAID configurations defined in the Common RAID Disk Drive Format standard, which is maintained by the Storage Networking Industry Association
RAID (/ r eɪ d /; redundant array of inexpensive disks or redundant array of independent disks) [1] [2] is a data storage virtualization technology that combines multiple physical data storage components into one or more logical units for the purposes of data redundancy, performance improvement, or both.
The reason for this huge difference lies in geom_raid5's design. In order to write data to a RAID5 volume, data must often first be read in order to calculate the parity information that protects against data loss in case of a single disk failure. Using request combining a full stripe block can be 'collected' so a read is no longer required.
Those RAID systems made their way to the consumer market, for users wanting the fault-tolerance of RAID without investing in expensive SCSI drives. Fast consumer drives make it possible to build RAID systems at lower cost than with SCSI, but most ATA RAID controllers lack a dedicated buffer or high-performance XOR hardware for parity calculation.
A flawed RAID 5/6 also exists, but can result in data loss.) [10] For RAID 1, the devices must have complementary sizes. For example, a filesystem spanning two 500 GB devices and one 1 TB device could provide RAID1 for all data, while a filesystem spanning a 1 TB device and a single 500 GB device could only provide RAID1 for 500 GB of data.