Promise Technology FastTrak66 Anwenderhandbuch Seite 53

Manual EN 05-08-1999 11:30
Understanding Disk Array Concepts
Striping/Mirror (RAID 0+1)
A combination of both above array types. It can increase performance by rea-
ding and writing data in parallel while protecting data with duplication. A
minimum of four drives needs to be installed. With a four-drive disk array, two
pairs of drives are striped. Each pair mirrors the data on the other pair of stri-
ped drives. The data capacity is similar to a standard Mirroring array with half
of total capacity dedicated for redundancy.
Dual Data Redundancy
One unique (though rarely occurring) feature of RAID 0+1 is dual fault tole-
rance. This allows two drives to fail simultaneously and still maintain the inte-
grity of data. There are six combinations in which two drives can fail;
FastTrak66 protects the data array in four of them for most drives (some drives
do not permit the Slave drive to continue to function if the Master drive fails).
Assume the drives are configured as follows (M = Master, A/B indicates which
striped pair the drive belongs to, # indicates which part of stripe data):
IDE 1
M Drive A1
S Drive B2
Under RAID 0+1, the array maintains data integrity if any 1&2 combination
survives.
Event Failed Drives
1 A1/A2
2 B2/B1
3 A1/B2
4 B1/A2
5 A1/B1
6 B2/A2
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IDE 2
Drive B1
Drive A2
Array Status Why?
Working B1/B2 retain array integrity
Working A1/A2 retain array integrity
Working B1/A2 retain array integrity
Working A1/B2 retain array integrity
Offline B2/A2 contain only half of array data
Offline A1/B1 contain only half of array data
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