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Chapter 4 Hardware Configuration 71
Disk Concatenation
Disk concatenation is a method for increasing logical volume size beyond the
capacity of one disk drive by creating one large metadevice from two or more
smaller drives. This lets you create arbitrarily large partitions.
Using this method, the concatenated disks are filled with data sequentially, with the
second disk being written to when no space remains on the first, the third when no
room remains on the second, and so on.
Disk Mirroring: RAID 1
Disk mirroring is a technique that uses data redundancy—two complete copies of all
data stored on two separate disks—to protect against loss of data due to disk failure.
One metadevice is created from two disks.
Whenever the operating system needs to write to the mirrored metadevice, both
disks are updated. The disks are maintained at all times with exactly the same
information. When the operating system needs to read from the mirrored
metadevice, it reads from whichever disk is more readily accessible at the moment.
The scheme is sometimes called RAID 1, where RAID stands for redundant arrays of
inexpensive disks.
RAID 1 offers the highest level of data protection, but storage costs are high, since all
data is stored twice.