Question

You have a set of four drives configured as RAID-5.

Drive #3 has crashed, but you have the data from Drives 1, 2, and 4 as shown here:

Drive #1: 01001111 01101000 01001110 01101111

Drive #2: 01011001 01110101 01110000 00100001

Drive #3: XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX

Drive #4: 01001111 01111100 01000111 01101111

What is the missing data in ASCII? Explain how you retrieved the information.

Answer 1

All drives are divided into four parts and each part contains 8-bit of data or parity according to RAID-5 standard configuration rules: Any part is calculated by XOR operation on rest 3-part of other disk respectively. Using this property we can calculate   the missing data.

Drive 1: Part1 = 01001111 (data)

Drive 2: Part1 = 01011001 (data)

Drive 3: Part1 = 01011001 (data)

Drive 4: Part1 = 01001111 (parity)

Drive 1: Part2 = 01101000 (data)

Drive 2: Part2 = 01110101 (data)

Drive 3: Part2 = 01100001 (parity)

Drive 4: Part2 = 01111100 (data)

Drive 1: Part3 = 01001110 (data)

Drive 2: Part3 = 01110000 (parity)

Drive 3: Part3 = 01111001 (data)

Drive 4: Part3 = 01000111 (data)

Drive 1: Part3 = 01101111 (parity)

Drive 2: Part3 = 00100001 (data)

Drive 3: Part3 = 00100001 (data)

Drive 4: Part3 = 01101111 (data)

Missing data :

Disk 3 :    01011001 01100001 01111001 00100001

ASCII value:   Y a y !