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Related to RAID 1: RAID 10, RAID 5


(Redundant Array of Independent Disks Mode 1) A popular disk 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 ?
RAID 5, the most prevalent configuration today, is much less expensive than RAID 1.
It has a unique auto-rebuilding feature that in the event of a drive failure in RAID 1 will rebuild the lost data while allowing access to the other drive, a powerful way to protect critical data.
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.
IDE: RAID 1 (with two or more drives) and IDE RAID 5 (with three or more drives) permits a failed drive to be pulled out of the PC enclosure and a new drive swapped for it without stopping the system.