Disk Array Terms - Promise Technology FASTTRAK66 User Manual

Manual EN 05-08-1999 11:30
Understanding Disk Array Concepts

Disk Array Terms

Disk Array Description
A "disk array" is formed from a group of 2 or more disk drives which appear
to the system as a single drive. The advantage of an array is to provide better
throughput performance and/or data fault tolerance. Better performance is
accomplished by sharing the workload in parallel among multiple physical dri-
ves. Fault tolerance is achieved through data redundant operation where if one
(or more) drive fails or has a sector failure, a mirrored copy of the data can be
found on another drive(s).
For optimal results, select identical Ultra ATA/66 drives to install in disk
arrays. The drives' matched performance allows the array to function better
as a single drive.
Disk Array Member
The individual disk drives in an array are called "members." Each member of
a specific disk array is coded in their "reserved sector" with configuration
information that identifies the drive as a member.
Disk Array Types
For most installations, the FastBuildTM setup "<1> Auto Setup" option will
configure your system.
There are four disk array types in three categories that can be installed on the
FastTrak66 card. Striping is in the Performance category while Mirroring,
Striping/Mirroring are in the Fault Tolerance category. Spanning (JBOD) is in
the Capacity category.
Disk arrays within the Performance and Fault Tolerance categories conform
with the Redundant Array of Independent Disks technology, or RAID. The
RAID levels supported are 0, 1, and 0/1.
Raid level
Raid 0 (Striping)
Raid 1 (Mirroring)
Raid 0+1( Stripe/Mirror) Best / High
JBOD ( Spanning)
All disk members in a formed disk array are recognized as a single physical
drive to the system.
Pagina 46
Read / Write Redundancy
Performance Capacity
Best / Best -----
High / Normal 50% min
50% min
Normal / Normal -----
46
Number
of Drives
2 to 4
2
4
2 to 4