Promise Technology FastTrak TX2300 User Manual download pdf (Page 99)

Chapter 6: Technology

RAID 1 – Mirror

When a logical drive is mirrored, identical data is written to a pair of disk drives,

while reads are performed in parallel. The reads are performed using elevator

seek and load balancing techniques where the workload is distributed in the most

efficient manner. Whichever drive is not busy and is positioned closer to the data

will be accessed first.

With RAID 1, if one disk drive fails or has errors, the other mirrored disk drive

continues to function. This is called Fault Tolerance. Moreover, if a spare disk

drive is present, the spare drive will be used as the replacement drive and data

will begin to be mirrored to it from the remaining good drive.

Figure 2. RAID 1 Mirrors identical data to two drives

Due to the data redundancy of mirroring, the capacity of the logical drive is only

the size of the smallest disk drive. For example, two 100GB disk drives which

have a combined capacity of 200GB instead would have 100GB of usable

storage when set up in a mirrored logical drive. Similar to RAID 0 striping, if disk

drives of different capacities are used, there will also be unused capacity on the

larger drive.

RAID 1 logical drives on the FastTrak TX Series consist of two disk drives.

Data Mirror

Disk Drives

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Promise Technology FastTrak TX2300 User Manual Page 99