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How to build a 100% Realtime Mirror of a SCO 5.0.5 box - SCO

Hi, I want to mirror by SCO BOX , how can I do that !. I have 2 exactly the same machines side by side (HP's TC4100 with and external Ultra SCSI3 port (that I think I can use to connect between the 2?!) . So that if the UPS (uninterrupted power supply) on one of the machines has hardware malfunction and kills the SCO filesystem badly (has happened to me), the other machine working under a different UPS has the same information up to the last minute! That way I can transfer the HARD DRIVES from one to the ...

  1. #1

    Default How to build a 100% Realtime Mirror of a SCO 5.0.5 box

    Hi,

    I want to mirror by SCO BOX , how can I do that !. I have 2 exactly the same
    machines side by side (HP's TC4100 with and external Ultra SCSI3 port (that
    I think I can use to connect between the 2?!) .
    So that if the UPS (uninterrupted power supply) on one of the machines has
    hardware malfunction and kills the SCO filesystem badly (has happened to
    me), the other machine working under a different UPS has the same
    information up to the last minute! That way I can transfer the HARD DRIVES
    from one to the other and be up and running in a couple of minutes.


    Enrique Guest

  2. #2

    Default Re: How to build a 100% Realtime Mirror of a SCO 5.0.5 box

    On Thu, 18 Sep 2003 21:50:17 +0100, Enrique Arredondo wrote
    (in message <dUoab.4069$news.prodigy.com>):
     

    Whilst it is possible to conenct two machines by SCSI, I doubt if the drivers
    have support for this - it requires that the drivers for one of the cards
    configure it for a non-standard device ID, and operate as a slave device (the
    other would be the bus master).

    Having got round this issue, you would then need another layer of drivers to
    enable the machines to talk to each other through this link - and I've not
    heard of this being done (at least at this end of the market).

    It may be easier to put a pair of gigabit ethernet ports, or fibre channel
    ports, or similar that have networking drivers. Ultra SCSI is only 40MB/s (or
    is it 80 MBps ?), or 320Mbps (640 Mbps) - gigabit ethernet would actually be
    faster !

    Having got the machines to talk, you then have the problem of mirroring them.
    I do not think that there is provision in the OS for that, on the other hand
    it may be possible (depending on your application) for some of the database
    systems to mirror the databases (or at least send frequent update transaction
    logs over).
     

    I'm not quite with you, you talk about mirroring the machines, but then you
    talk about transferring the hard drives - if you transfer the hard drives
    then you will transfer the filesystem corruption that is on them !

    You can minimise the risk by making sure that you use a journalling
    filesystem - I believe OpenServer 5.0.6 does this, I don't know when it was
    introduced, and you don't say what version you are running.

    Even this does not get you out of trouble, since you will always have the
    issue of what happens if the application is updating data and half of the
    transaction is done when the power stops (or whatever event it is). If if you
    have no filesystem corruption, you can have a partially updated database with
    all the issued that causes - I know, I've been there* :-(

    Simon

    * In our case, there was a bug in the driver for the RAID controller in our
    new IBM X250 - this resulted in disk accesses failing (only VERY
    infrequently), and the block in question becoming 'locked' due to the request
    never completing (the driver believed it had 'finished' by reporting an
    error, the OS was still waiting for the request to complete). This also
    caused any process accessing the block to halt in an unkillable way (I assume
    in a kernel level call). Any further access of this disk block by any other
    process would halt the process as the OS would be waiting for the access to
    complete.

    One day, one such 'locked' block was in a critical area, and over a period of
    a few hours, more and more processes stopped until the machine just locked up
    - no kernel panic, it just stopped. After a reboot we determined that the
    application had inconsistently written partial updates - or rather some files
    had been updated, others had not been.

    Having a perfect mirror of this data would not have helped !

    Simon Guest

  3. #3

    Default Re: How to build a 100% Realtime Mirror of a SCO 5.0.5 box

    Enrique Arredondo wrote:
     

    I have no experience with this, but try:

    http://www.savwareha.com/

    /dev/null Guest

  4. #4

    Default Re: How to build a 100% Realtime Mirror of a SCO 5.0.5 box

    Enrique,

    I believe the following software packages
    are all available for OpenServer:

    1776 Fault-Freedom II
    http://www.1776soft.com/

    SavWareHA
    http://www.savwareha.com/

    and the new guys on the block....

    HA Technical Solutions
    http://www.tech-sol.com

    Each company advertises that they do what you need.
    The last may require a recent version of OSR5
    that is able to run Java 1.3.1 or later.

    Regards,

    -louis


    "Enrique Arredondo" <net> wrote in message news:<dUoab.4069$news.prodigy.com>... 
    Louis Guest

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