Synchron Plexes with VxWM - Veritas Volume Manager

This is a discussion on Synchron Plexes with VxWM - Veritas Volume Manager ; Will VxVM will acknowledge a synchron write (on a file open with option O_SYNC) on multiple plexes (mirrors) of a volume when the first plex is written or when all plexes are written? Can you configure it? When VxVM acknowledge ...

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Thread: Synchron Plexes with VxWM

  1. Synchron Plexes with VxWM


    Will VxVM will acknowledge a synchron write (on a file open with option O_SYNC)
    on multiple plexes (mirrors) of a volume when the first plex is written or
    when all plexes are written? Can you configure it?

    When VxVM acknowledge the IO after the first plex write, the write order
    can not be garantueed an may leed to inconsitent file systems or Oracle Databases...

  2. Re: Synchron Plexes with VxWM

    The FS will handle the sync or async writing.

    The volume will ack as soon as the data is written on the first plex (it
    then kicks off a background process to sync). This can not be configured.


    See the man page for vxfs mount options of Osync options (man
    vxfs_mount) or see the VxFS User's Guide




    Andreas Zallmann wrote:
    > Will VxVM will acknowledge a synchron write (on a file open with option O_SYNC)
    > on multiple plexes (mirrors) of a volume when the first plex is written or
    > when all plexes are written? Can you configure it?
    >
    > When VxVM acknowledge the IO after the first plex write, the write order
    > can not be garantueed an may leed to inconsitent file systems or Oracle Databases...


  3. Re: Synchron Plexes with VxWM


    Hello,

    Were can i found out the exact behaviour of volumes with a plex? We need
    to be 100% sure of data consistency with plexes.....

    Regards.






    Me wrote:
    >The FS will handle the sync or async writing.
    >
    >The volume will ack as soon as the data is written on the first plex (it


    >then kicks off a background process to sync). This can not be configured.
    >
    >
    >See the man page for vxfs mount options of Osync options (man
    >vxfs_mount) or see the VxFS User's Guide
    >
    >
    >
    >
    >Andreas Zallmann wrote:
    >> Will VxVM will acknowledge a synchron write (on a file open with option

    O_SYNC)
    >> on multiple plexes (mirrors) of a volume when the first plex is written

    or
    >> when all plexes are written? Can you configure it?
    >>
    >> When VxVM acknowledge the IO after the first plex write, the write order
    >> can not be garantueed an may leed to inconsitent file systems or Oracle

    Databases...


  4. Re: Synchron Plexes with VxWM

    Behaviour of plexes can be found in Volume Manager documentation, Volume
    Manager training.


    Now, do you think that Veritas would have been in bussiness for more
    than 15 years if the plexes were not up to date ?


    The only way to see if plexes are up to date:

    1. Stop the volume
    2. detach 1 plex
    3. start the volume with 1 plex only
    4. get a checksum (well, this is up to you how you do this step)
    5. Stop the volume
    6. Detach the plex
    7. Attach the other plex
    8. Get a checksum and compare with the previous checksum


    Warnings:
    ---------
    1. If you mount the filesystem at any stage, will get different checksums !
    2. You will have to stop production to do these tests



    There is another way. A snapshot is another plex where you can break it
    off (snap it off) without stopping volumes. Then you can mount the
    snapshot and inspect the data.


    All of the above is in the doco



    At Aalberts wrote:
    > Hello,
    >
    > Were can i found out the exact behaviour of volumes with a plex? We need
    > to be 100% sure of data consistency with plexes.....
    >
    > Regards.
    >
    >
    >
    >
    >
    >
    > Me wrote:
    >
    >>The FS will handle the sync or async writing.
    >>
    >>The volume will ack as soon as the data is written on the first plex (it

    >
    >
    >>then kicks off a background process to sync). This can not be configured.
    >>
    >>
    >>See the man page for vxfs mount options of Osync options (man
    >>vxfs_mount) or see the VxFS User's Guide
    >>
    >>
    >>
    >>
    >>Andreas Zallmann wrote:
    >>
    >>>Will VxVM will acknowledge a synchron write (on a file open with option

    >
    > O_SYNC)
    >
    >>>on multiple plexes (mirrors) of a volume when the first plex is written

    >
    > or
    >
    >>>when all plexes are written? Can you configure it?
    >>>
    >>>When VxVM acknowledge the IO after the first plex write, the write order
    >>>can not be garantueed an may leed to inconsitent file systems or Oracle

    >
    > Databases...
    >


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