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MaxAttach NAS 6000 Administration Guide
RAID 1 Mirroring
Description
In RAID 1 mirroring, the RAID controller totally duplicates the data writes on two drives
at once, providing 100% data redundancy. If one drive fails, the second drive carries on as
before with reads and writes until a replacement drive can be added for a data restore.
RAID 1 has been used longer than any other form of RAID.
Depending on the system, either the drives, or the drives and their controllers are
duplicated.
Fault Tolerance Cost
RAID 1 is fully fault tolerance but carries a 50% disk space cost to implement.
Performance
RAID 1 arrays may use parallel access for high transfer rate when reading. More
commonly, RAID 1 array disks operate independently and improve performance for
read-intensive applications, but at relatively high inherent cost. If one drive drops offline,
read/write performance is the same until the rebuild process starts. During restores,
performance can be degraded as the drive controller rebuilds the replacement disk drive.
Application Focus
RAID 1 practical use is usually limited to applications where fault tolerance is required,
regardless of cost. This is used primarily in high reliability systems where constant
availability is required.
Array Size
RAID 1 array disks are always in pairs. Two disk arrays can be mirrored using a common
technique, described below, called RAID 0 + 1 where a stripped array of multiple disks is
then mirrored. This technique is used in the MaxAttach NAS 6000 O/S images on drive
C:\ and D:\.
Chapter #11 - Appendix - Disk Array RAID Concepts
11/07/01 -- Revision 2.0.03A
Chapter #11 - Appendix - Disk Array RAID Concepts
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RAID 1 Mirroring
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