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In computing, the acronym RAID (originally from the Redundant Array of Inexpensive Disks, now also Redundant Array of Independent Disks, refers to a storage system computer that uses multiple hard disks between which it distributes or replicates the data. Depending on its configuration (commonly referred to as a "level"), the benefits of a RAID over a single disk are one or more of the following: higher integrity, better fault tolerance, more throughput, and more capacity. In its original implementations, its key advantage was the ability to combine several low-cost devices and older technology into one that offered greater capacity, reliability, speed or a combination of these than a single, next-generation, higher-cost device.
Professional hosting strengthens your backup servers by applying a RAID1:
A RAID 1 creates an exact copy (or mirror) of a data set on two or more disks (array). This is useful when read performance is more important than capacity and also from the security point of view, since a RAID 0 for example is not tolerant to the failure of one of the disks, whereas a RAID 1 yes, to have the same information on each disk.
A RAID 1 array is as large as the smallest of its disks. A classic RAID 1 consists of two disks in mirror, which increases exponentially the reliability with respect to a single disc; that is, the probability of failure of the set is equal to the product of the failure probabilities of each of the disks (because in order for the set to fail it is necessary that all its disks do).
In addition, since all data is on two or more disks, with customarily independent hardware, the read performance is increased approximately as a linear multiple of the number of copies; that is, a RAID 1 can be simultaneously reading two different data on two different disks, so its performance is doubled. To maximize the benefits of RAID 1 performance, we recommend the use of separate disk controllers, one for each disk (a practice called splitting or duplexing).
As in RAID 0, the average read time is reduced, as the sectors to be searched can be divided between the disks, lowering the search time and raising the transfer rate, with the only limit of the speed supported by the RAID controller . However, many older IDE RAID 1 cards read only from one pair disk, so their performance is equal to that of a single disk. Some older RAID 1 deployments also read from both disks simultaneously and compare the data to detect errors. The detection and correction of errors in modern hard disks make this practice little useful.
When writing, the array behaves as a single disk, since the data must be written to all RAID 1 disks. Therefore, the performance does not improve.
RAID 1 is an appropriate system in environments where availability is critical 24 hours a day. Apart from the mirrored disks that create the array in RAID 1 we can mark additional disks as a backup. These can be defined as hot spare if we want them to be in operation or standby hot spare, if we want them to be in standby mode. When one of the mirror disks fails, one of the backup disks becomes part of the array of mirror disks (it instantly enters if it is a hot spare disk or it takes a few moments if it has to boot as a disk standby hot spare), doubling the information on it. This requires that the management application of the set supports the recovery of the data of the disk at the time of the division, procedure called rebuilding. This is less critical than the presence of a snapshot feature on some file systems, where some space for changes is reserved, presenting a static view at a given time point of the file system. Alternatively, a set of disks may be stored in a similar fashion as is done with traditional tapes.