Fault tolerance

Posted on 2006-04-06
Last Modified: 2010-04-03
This is a question from a MCSE book

You administer a server called Server1 which has a single physical disk that is configured as a simple volume

You plan to store the files for a large database on the server. You plan to install additional physical disks on the server

You need to configure the disks on the server so it provides fault tolerance for the operating system and the database files.

The answer says install 3 additional disks and create a new RAID-5 volume, and place the database files on the new volume


Install another disk and configure the simple volume as a mirrored volume

My question is: - Why three extra disks for the RAID-5,


Why do u need the Additional disk for the mirrored volume
Question by:LFC1980
    LVL 9

    Accepted Solution

    3 is the minimum number for a RAID 5 array. Reason being that data is stripped across 2 disks and parity check bits are stored on the 3rd. In Theory if a disk fails then you can recreate the data from half the stripe and the parity. If Parity fails, you still have the data. In reality, this is short sighted and you should use more disks to provide faster recovery and hot standby disk to give zero impact in case of a failure. You can also stripe the parity across all drives to provide slightly better recovery.
    You have no resilience in a single drive. Therefore, the mirror pair allows for a single drive to fail without impact.

    Hope this helps.... or where you asking something else?

    Author Comment


    i get ya

    the one that was in the machine will be used with the extra single one to make a mirror pair.

    and the 3 extra will be for RAID 5....correct ?
    LVL 4

    Expert Comment


    Author Comment


    Thanks for confirming that, danhill85

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    6 Surprising Benefits of Threat Intelligence

    All sorts of threat intelligence is available on the web. Intelligence you can learn from, and use to anticipate and prepare for future attacks.

    In this article, I provide some information on storage disks which go into calculations that will help you figure out how much Input/output Operations Per Second (IOPS) your disk subsystem can deliver. To effectively size & tune up applications l…
    How to update Firmware and Bios in Dell Equalogic PS6000 Arrays and Hard Disks firmware update.
    This tutorial will walk an individual through the process of installing the necessary services and then configuring a Windows Server 2012 system as an iSCSI target. To install the necessary roles, go to Server Manager, and select Add Roles and Featu…
    This Micro Tutorial will teach you how to reformat your flash drive. Sometimes your flash drive may have issues carrying files so this will completely restore it to manufacturing settings. Make sure to backup all files before reformatting. This w…

    760 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    10 Experts available now in Live!

    Get 1:1 Help Now