RE: What is Quorum device ?

From: Dave Morgan <dave.morgan_at_cybersurf.net>
Date: Fri, 08 Jun 2001 09:51:42 -0700
Message-ID: <F001.0032280B.20010608095654@fatcity.com>

Hi Sinardy,

        The following is from IBM on one of there SSA's 
        (Serial Storage Array, similar to RAID, different
        hardware implementation)

        Assuming you have a form of mirrored disk with two
        disks for each mirror then a Qurorum setting of
        2 would require both disks to be available and containing
        matching information before the device will show upon boot. 
        Therefore always leave quorum set at 1 otherwise the 
        mirroring will not improve your availability.

        If the mirror involves 3 disks then Quorum determines
        how many of the disk need to be available before allowing
        access to the disks. A setting of 2 requires 2 of the disks 
        to be available etc, etc, etc.

        Unless your system is critical, life or death, (ie: medical
        information, realtime air traffic control etc) there is really
        no need to set quorum larger than 1. If the info is critical 
        and verification of data accuracy is required then at least
        triple mirror and set quorum at (# of mirrors - 1)

        <EVIL>
        For a junior dba or sysadmin, (on a test box) 
                shutdown the db
                set quorum = # of disks in the mirror, 
                dd one of the datafile blocks on one of the disks
                reboot the box
                and ask him/her 
                        - sysadmin, make the array accessible
                        - dba, bring up the database
                tell all the sysadmins/network admins to watch the fun
        </EVIL>

        It's a cruel but effective piece of training

HTH
Dave

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Dave Morgan
DBA, Cybersurf
Office: 403 777 2000 ext 284
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Author: Dave Morgan
INET: dave.morgan_at_cybersurf.net

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