RAID 1


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Related to RAID 1: RAID 10, RAID 5

RAID 1

(Redundant Array of Independent Disks Mode 1) A popular disk or solid state drive (SSD) subsystem that increases safety by writing the same data on two drives. Called "mirroring," RAID 1 does not increase performance. However, if one drive fails, the second drive is used, and the failed drive is manually replaced. After replacement, the RAID controller duplicates the contents of the working drive onto the new one. See RAID 10 and RAID.


Mirroring for Fault Tolerance



Widely used, mirroring writes two drives at the same time so that data are duplicated. It provides the highest reliability, but doubles the number of drives needed.



RAID 1 Probability of Failure
The more drives in a RAID 1 array, the lower the probability of failure. For example, if experience tells us that one out of a thousand drives fails in a year, the probability that an entire 2-drive array will fail in a year is 1 in a million; that an entire 3-drive array will fail is 1 in a billion and so on.

The formula: if the probability of failure of each of n drives is p, then the probability that all the drives will fail is p^n.
References in periodicals archive ?
Obviously, RAID 1 represents a significant redundancy in protecting your data and applications, though implementing a RAID 1 array doesn't mean that you should forego other backup arrangements.
MegaRAID ATA 133-2 RAID enhances performance for data striping (RAID 0), data redundancy (RAID 1), and mirroring with striping (RAID 10).
RAID 1 is commonly used to protect critical information by mirroring all data on one drive to another drive to provide higher availability for mission-critical data.
Users can easily plug a Maxtor SATA drive directly into a VT8237-enabled motherboard for single, SATA hard drive performance, or install two drives for a RAID 0 or RAID 1 configuration for a significant performance improvement or added data protection."
The entry- level AAA-131U2 Ultra2 SCSI RAID card provides robust data backup reliability with RAID 1 and RAID 5 structure for Seiko Epson's Windows 2000-based, next-generation ERP systems.
The number of back-end I/Os per application write is always two for RAID 1; in OLTP applications it is generally four for RAID 5 and six for RAID 6.