Promise Technology FastTRAK66, Руководство пользователя

Страница: 50 / 73

Understanding Disk Array Concepts
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.
Dual Data Redundancy
One unique (though rarely occurring) feature of RAID 0+1 is dual fault tolerance.
This allows two drives to fail simultaneously and still maintain the integrity 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 IDE2
M Drive A1 Drive B1
S Drive B2 Drive A2
Under RAID 0+1, the array maintains data integrity if any 1&2 combination survives.
Event Failed Drives Array Status Why?
1 A1/A2 Working B1/B2 retain array integrity
2 B2/B1 Working A1/A2 retain array integrity
3 A1/B2 Working B1/A2 retain array integrity
4 B1/A2 Working A1/B2 retain array integrity
5 A1/B1 Offline B2/A2 contain only half of array data
6 B2/A2 Offline A1/B1 contain only half of array data
Spanning (JBOD)
6-5