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TekSpek 's
RAID
Date issued:
RAID 1: Mirroring
Mirroring is one method of improving reliability of data
storage (the other being parity), the idea is to build in redundancy
by writing data to two or more disks simultaneously, hence the term
“mirror”. Not only does mirroring provide 100% redundancy
in case of disk failure but recovery is fairly swift should a disk
fail because all the data is immediately accessible from another
disk. Generally, performance is adversely affected by using a mirrored
array; some forms of read performance are increased but write performance
is decreased as the data is written more than once.
The major drawback for a mirrored array is the overheads in disk space wastage; half the total capacity of the hard drives is lost in providing redundancy, although with hard drives prices falling all the time a fairly large mirrored array can be obtained for a reasonable cost. Newer SATA drives and SCSI drives with hotplug ability mean that should a drive fail under RAID 1 the faulty drive can be removed and replaced without shutting down the entire system, which is very useful where large quantities of data are stored and uptime is important.
