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ISRO CSE 2007 | Question: 56

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13 13 votes

RAID levels comparison chart

    RAID 1 RAID 5 RAID 6  
Min number of disks   2 3 4  
Fault to­le­ran­ce   1 disk 1 disk 2 disks  
Disk space over­head   50% 1 disk 2 disks  
Read speed   Fast Slow,   
Write speed   Fair Slow,  Fair
Hard­ware cost   High (disks) High Very high

RAID levels 2, 3, and 4 are theoretically defined but not used in practice. so ans should be A

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  • RAID 1 (Mirroring): Every block is written to two disks.
    → Read: Super fast, because you can read from either disk (sometimes even parallel).
    → Write: Just copy the same data to both disks. No parity, no calculation. So write is not slowed down.

  • RAID 3, 4, 5, 6: All of these use parity.
    → Every write requires extra steps: read old data + read old parity + calculate new parity + write new data + write new parity.
    → That’s why writes are slower.

So, the correct answer is RAID 1 ✅

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