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Witness server- DATABASE MIRRORING RRS feed

  • Question

  • I have read that in high-safety mode, the witness will become the principal if the principal server goes down, BUT
    I thought the witness was there to mediate the automatic failover from principal to secondary mirrored server if the
    principal machine goes down.
    Can anyone clarify...? appreciate it.

    Wednesday, December 2, 2009 4:06 PM

Answers

  • Witness server role:

    In the database mirroring topology you may have an optional third server called the witness. Witness server is required for enabling automatic failover from principal to mirror server or vice-versa. Unlike principal and mirror servers, the witness server does not serve the database. The role of the witness is to verify whether a given partner server is up and functioning. Supporting automatic failover is the only function for witness server. It uses quorum to identify which server holds the principal copy and which server holds the mirror copy of the database.

    --------------------------
    Thanks,Suhas V

    Thursday, December 3, 2009 2:29 AM

All replies

  • The Witness server does not become the Principal. It is only there to agree with the Mirror server that the Principal is down.
    Ken Simmons
    http://cybersql.blogspot.com
    http://twitter.com/kensimmons
    • Proposed as answer by VidhyaSagar Thursday, December 3, 2009 10:04 AM
    Wednesday, December 2, 2009 4:17 PM
  • The witness simply supports automatic failover by verifying whether the principal server is up and functioning. The mirror server initiates automatic failover only if the mirror and the witness remain connected to each other after both have been disconnected from the principal server.
    Thanks, Leks
    Wednesday, December 2, 2009 4:46 PM
    Answerer
  • Witness server role:

    In the database mirroring topology you may have an optional third server called the witness. Witness server is required for enabling automatic failover from principal to mirror server or vice-versa. Unlike principal and mirror servers, the witness server does not serve the database. The role of the witness is to verify whether a given partner server is up and functioning. Supporting automatic failover is the only function for witness server. It uses quorum to identify which server holds the principal copy and which server holds the mirror copy of the database.

    --------------------------
    Thanks,Suhas V

    Thursday, December 3, 2009 2:29 AM
  • What are the ramifications if the witness goes down????

     

    THanks,
    John

    Tuesday, June 21, 2011 12:29 PM
  • What are the ramifications if the witness goes down????

     

    THanks,
    John


    This mode is reffered as "A partner-to-partner quorum that consists of the two partners"

    As long as the partners retain quorum, the database continues in a SYNCHRONIZED state, and manual failover remains possible. Without the witness, automatic failover is not possible; but when the witness regains quorum, the session resumes regular operation, and automatic failover is supported again.

     


    Thanks, Leks
    Tuesday, June 21, 2011 8:47 PM
    Answerer