Sun Microsystems 220R manual Disk Concatenation, Disk Mirroring RAID

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.

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