Promise Technology FAST TRAK100TM - Manual (Page 73)

FastTrak100 User Manual
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Striping/Mirror (RAID 0+1)
A combination of both above array types. It can increase performance by reading
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 striped drives. The data
capacity is similar to a standard Mirroring array with half of total capacity dedicated
for redundancy.
About Dual Data Redundancy
One unique (though rarely occurring) feature of RAID 0+1 is dual fault tolerance. In
some cases, two drives can fail simultaneously and still maintain the integrity of
data. There are six combinations in which two drives can fail. FastTrak100 protects
the data array in four of those cases depending on drive type (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 IDE2
M Drive A1 Drive B1
S Drive B2 Drive A2