08-12
26

The Common RAID levels—RAID 1

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AuthorEASEUS   Category Basic Computing Guide   Comments0   Post Time 2008-12-26 03:01:43 -0500

RAID 1, creates an exact copy of a set of data on two or more disks. It provides fault tolerance from disk errors and failure of all but one of the drives. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing.


The read performance in RAID 1 can go up roughly as a linear multiple of the number of copies, because all the data exists in two or more copies, each with its own hardware, that is, a RAID 1 array of two drives can be reading in two different places at the same time, though not all implementations of RAID 1 do this. To maximize performance of RAID 1, independent disk controllers are recommended, one for each disk.


RAID 1 has many administrative advantages. For instance, in some environments, it can "split the mirror": declare one disk as inactive, do a backup of that disk, and then "rebuild" the mirror. This is useful in situations where the file system should be constantly available. This requires that the application supports recovery from the image of data on the disk at the point of the mirror split. This procedure is less critical in the presence of the "snapshot" feature of some file systems, in which some space is reserved for changes, presenting a static point-in-time view of the file system. Alternatively, a new disk can be substituted so that the inactive disk can be kept in much the same way as traditional backup.

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