What is RAID-5

**rehanshabbir** · 25th April 2009, 11:49 PM

RAID-5 is very popular in todays server machines. I am just Elaborating the magic of this technology so to get the detail knowledge about disk failure rate, perforamance and data recovery techniques you can visit sites like wikipedia.org I'll try to go on simple and smooth way to make my thread understandable.

In raid-5 minimum 3 disks of same size and specification are used. I am using 3 disk scenario in my post. Fore example if we use 3 disks of 300GB our total disk space equals 900GB but in raid-5 we get 600GB for data and 300 GB for making RAID. Raid-5 uses XOR logical gate. We know that all data in computer is manipulated in binary so data bits are distributed over 2 disks and the result of XOR of first 2 disks is placed over 3rd disk.
see the following example.

Disk 1 Disk 2 Disk 3 [disk1 XOR disk2]
0110 0011 1001

now consider if disk one fails, we raplace it with a new one then RAID controler device automaticly takes XOR of Disk 2 and Disk 3 and result is re-built over Disk 1. Same procedure occur if any one disk fails. It's the magic of XOR that by taking the XOR of bits of any two disks we will get the bits of
3rd one. I encourage you to practice it over paper.

Thanks and ragards.

**kashifazizawan** · 26th April 2009, 01:23 AM

nice sharing plz keep it up....

""now consider if disk one fails, we raplace it with a new one then RAID controler device automaticly takes XOR of Disk 2 and Disk 3 and result is re-built over Disk 1.""

i am confused at this statement plz explane,
if any one of the HDD fails then how can we add new one....

regards:-

**rehanshabbir** · 26th April 2009, 05:59 AM

If Server has hotplug hard disks, Its mean you can plug out defaulty harddisk from server in running condition. Otherwise you have to shut down server to change or replace hard disks. A dead hard disk has no further use, so we replace it with a new hard disk, after that RAID controler starts its work.

Please do not hasitate to ask if any further confusion.

best regards