User's Manual

Drive Arrays and Fault Tolerance

D-4 HP Smart Array 641/642 Controller User Guide

HP CONFIDENTIAL

Writer: John Turner File Name: l-appd drive arrays & fault tolerance

Codename: darkmatter -antimatter Part Number: 309311-001 Last Saved On: 11/6/02 4:34 PM

Figure D-4: Two arrays (A1, A2) containing five logical

drives spread across five physical drives

Each logical drive in an array is distributed across all of the physical drives within the

array. A logical drive can also extend across more than one port on the same

controller, but it cannot extend across more than one controller.

Drive failure, although rare, is potentially catastrophic. In Figure D-4, for example,

failure of any physical drive causes all logical drives in the same array to fail, and all

data on the drives is lost.

To protect against data loss due to physical drive failure, logical drives are

configured with fault tolerance. There are several fault-tolerance methods; those that

are described in this appendix are:

• RAID 0—Data Striping only (no fault tolerance)

• RAID 1+0—Drive Mirroring

• RAID 5—Distributed Data Guarding

• RAID ADG—Advanced Data Guarding