Promise FastTrack TX2000 - Page 5

RAID Levels - Page 2

- RAID 0+1 (Striping/Mirroring)

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.

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 left (M = Master, A/B indicates which striped pair the drive belongs to, # indicates which part of stripe data):

- JBOD (Spanning)

A Spanning disk array (also aptly named as JBOD for "Just a Bunch of Drives") is equal to the sum of all drives when the drives used are of different capacities. Spanning stores data on to a drive until it is full, then proceeds to store files onto the next drive in the array. There are no additional performance or fault tolerance array features in this array. When any disk member fails, the failure affects the entire array.